6K33

Structure of PSI-isiA supercomplex from Thermosynechococcus vulcanus

• PDB DOI: https://doi.org/10.2210/pdb6K33/pdb
• EM Map EMD-9908: EMDB EMDataResource

• Classification: PHOTOSYNTHESIS
• Organism(s): Thermostichus vulcanus
• Mutation(s): No 
• Membrane Protein: Yes  OPMmpstruc


• Deposited: 2019-05-16 Released: 2020-05-20 
• Deposition Author(s): Akita, F., Nagao, R., Kato, K., Shen, J.R., Miyazaki, N.

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Experimental Data Snapshot

• Method: ELECTRON MICROSCOPY
• Resolution: 2.74 Å
• Aggregation State: PARTICLE 
• Reconstruction Method: SINGLE PARTICLE 

Starting Model: experimental

Literature

Structure of a cyanobacterial photosystem I surrounded by octadecameric IsiA antenna proteins.

Akita, F., Nagao, R., Kato, K., Nakajima, Y., Yokono, M., Ueno, Y., Suzuki, T., Dohmae, N., Shen, J.R., Akimoto, S., Miyazaki, N.

(2020) Commun Biol 3: 232-232

• PubMed: 32393811 
• DOI: https://doi.org/10.1038/s42003-020-0949-6
• Primary Citation of Related Structures:  
  6K33


• PubMed Abstract: 
  

  Iron-stress induced protein A (IsiA) is a chlorophyll-binding membrane-spanning protein in photosynthetic prokaryote cyanobacteria, and is associated with photosystem I (PSI) trimer cores, but its structural and functional significance in light harvesting remains unclear. Here we report a 2.7-Å resolution cryo-electron microscopic structure of a supercomplex between PSI core trimer and IsiA from a thermophilic cyanobacterium Thermosynechococcus vulcanus. The structure showed that 18 IsiA subunits form a closed ring surrounding a PSI trimer core. Detailed arrangement of pigments within the supercomplex, as well as molecular interactions between PSI and IsiA and among IsiAs, were resolved. Time-resolved fluorescence spectra of the PSI-IsiA supercomplex showed clear excitation-energy transfer from IsiA to PSI, strongly indicating that IsiA functions as an energy donor, but not an energy quencher, in the supercomplex. These structural and spectroscopic findings provide important insights into the excitation-energy-transfer and subunit assembly mechanisms in the PSI-IsiA supercomplex.

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Organizational Affiliation: 

Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University, Okayama, 700-8530, Japan. [e-mail].

Biological Assembly 1  

Global Symmetry: Cyclic - C3  (Explore in 3D)
Global Stoichiometry: Hetero 54-mer - A18B3C3D3E3F3G3H3I3J3K3L3M3 Pseudo Symmetry: Cyclic - C3  (Explore in 3D)
Pseudo Stoichiometry: Hetero 54-mer - A18B6C6D3E3F3G3H3I3J3K3 

Biological assembly 1 assigned by authors.

Biological Assembly Evidence: microscopy

Macromolecule Content

• Total Structure Weight: 2,096.2 kDa 
• Atom Count: 137,634 
• Modelled Residue Count: 12,681 
• Deposited Residue Count: 13,452 
• Unique protein chains: 13

Macromolecules

Entity ID: 1
Molecule	Chains	Sequence Length	Organism	Details	Image
Photosystem I P700 chlorophyll a apoprotein A1	A [auth aA], KA [auth cA], S [auth bA]	755	Thermostichus vulcanus	Mutation(s): 0  EC: 1.97.1.12 Membrane Entity: Yes
UniProt
Find proteins for P25936 (Thermostichus vulcanus) Explore P25936  Go to UniProtKB:  P25936

Entity ID: 2
Molecule	Chains	Sequence Length	Organism	Details	Image
Photosystem I P700 chlorophyll a apoprotein A2	B [auth aB], LA [auth cB], T [auth bB]	740	Thermostichus vulcanus	Mutation(s): 0  EC: 1.97.1.12 Membrane Entity: Yes
UniProt
Find proteins for P0A409 (Thermostichus vulcanus) Explore P0A409  Go to UniProtKB:  P0A409

Entity ID: 3
Molecule	Chains	Sequence Length	Organism	Details	Image
Photosystem I iron-sulfur center	C [auth aC], MA [auth cC], U [auth bC]	80	Thermostichus vulcanus	Mutation(s): 0  EC: 1.97.1.12 Membrane Entity: Yes
UniProt
Find proteins for P0A417 (Thermostichus vulcanus) Explore P0A417  Go to UniProtKB:  P0A417

Entity ID: 4
Molecule	Chains	Sequence Length	Organism	Details	Image
Photosystem I reaction center subunit II	D [auth aD], NA [auth cD], V [auth bD]	138	Thermostichus vulcanus	Mutation(s): 0
UniProt
Find proteins for P0A422 (Thermostichus vulcanus) Explore P0A422  Go to UniProtKB:  P0A422

Entity ID: 5
Molecule	Chains	Sequence Length	Organism	Details	Image
Photosystem I reaction center subunit IV	E [auth aE], OA [auth cE], W [auth bE]	75	Thermostichus vulcanus	Mutation(s): 0

Entity ID: 6
Molecule	Chains	Sequence Length	Organism	Details	Image
Photosystem I reaction center subunit III	F [auth aF], PA [auth cF], X [auth bF]	164	Thermostichus vulcanus	Mutation(s): 0

Entity ID: 7
Molecule	Chains	Sequence Length	Organism	Details	Image
Photosystem I reaction center subunit VIII	G [auth aI], QA [auth cI], Y [auth bI]	38	Thermostichus vulcanus	Mutation(s): 0

Entity ID: 8
Molecule	Chains	Sequence Length	Organism	Details	Image
Photosystem I reaction center subunit IX	H [auth aJ], RA [auth cJ], Z [auth bJ]	41	Thermostichus vulcanus	Mutation(s): 0

Entity ID: 9
Molecule	Chains	Sequence Length	Organism	Details	Image
Photosystem I reaction center subunit PsaK	AA [auth bK], I [auth aK], SA [auth cK]	85	Thermostichus vulcanus	Mutation(s): 0  Membrane Entity: Yes
UniProt
Find proteins for P23318 (Thermostichus vulcanus) Explore P23318  Go to UniProtKB:  P23318

Entity ID: 10
Molecule	Chains	Sequence Length	Organism	Details	Image
Photosystem I reaction center subunit XI	BA [auth bL], J [auth aL], TA [auth cL]	154	Thermostichus vulcanus	Mutation(s): 0

Entity ID: 11
Molecule	Chains	Sequence Length	Organism	Details	Image
Photosystem I reaction center subunit XII	CA [auth bM], K [auth aM], UA [auth cM]	31	Thermostichus vulcanus	Mutation(s): 0

Entity ID: 12
Molecule	Chains	Sequence Length	Organism	Details	Image
Photosystem I reaction center subunit psaX	DA [auth bX], L [auth aX], VA [auth cX]	35	Thermostichus vulcanus	Mutation(s): 0

Entity ID: 13
Molecule	Chains	Sequence Length	Organism	Details	Image
Iron stress in-duced protein A	AB [auth c5], BB [auth c6], EA [auth b1], FA [auth b2], GA [auth b3], HA [auth b4], IA [auth b5], JA [auth b6], M [auth a1], N [auth a2], O [auth a3], P [auth a4], Q [auth a5], R [auth a6], WA [auth c1], XA [auth c2], YA [auth c3], ZA [auth c4]	358	Thermostichus vulcanus	Mutation(s): 0

Small Molecules

Ligands 8 Unique
ID	Chains	Name / Formula / InChI Key	2D Diagram
CLA	AAA [auth c1], AC [auth aA], ACA [auth c4], ADA [auth c5], AE [auth aB], AEA [auth c6], AG [auth a1], AH [auth a2], AI [auth a3], AJ [auth a4], AL [auth bA], AM [auth bA], AO [auth bB], AQ [auth b1], AR [auth b2], AS [auth b3], AU [auth b6], AV [auth cA], AW [auth cA], AX [auth cB], AY [auth cB], AZ [auth cJ], BAA [auth c1], BC [auth aA], BCA [auth c4], BDA [auth c5], BE [auth aB], BEA [auth c6], BG [auth a1], BH [auth a2], BI [auth a3], BJ [auth a4], BK [auth a5], BL [auth bA], BM [auth bA], BN [auth bB], BO [auth bB], BQ [auth b1], BR [auth b2], BS [auth b3], BT [auth b4], BU [auth b6], BV [auth cA], BW [auth cA], BX [auth cB], BY [auth cB], BZ [auth cJ], CAA [auth c1], CBA [auth c2], CC [auth aA], CCA [auth c4], CDA [auth c5], CE [auth aB], CEA [auth c6], CG [auth a1], CH [auth a2], CI [auth a3], CJ [auth a4], CL [auth bA], CM [auth bA], CN [auth bB], CO [auth bB], CP [auth bF], CQ [auth b1], CR [auth b2], CS [auth b3], CU [auth b6], CV [auth cA], CW [auth cA], CX [auth cB], CY [auth cB], DAA [auth c1], DB [auth aA], DC [auth aA], DCA [auth c4], DDA [auth c5], DE [auth aB], DEA [auth c6], DG [auth a1], DH [auth a2], DI [auth a3], DJ [auth a4], DL [auth bA], DM [auth bA], DN [auth bB], DO [auth bB], DQ [auth b1], DR [auth b2], DT [auth b5], DU [auth b6], DV [auth cA], DW [auth cA], DX [auth cB], DY [auth cB], EB [auth aA], EBA [auth c3], EC [auth aA], ECA [auth c4], ED [auth aB], EDA [auth c5], EE [auth aB], EEA [auth c6], EG [auth a1], EH [auth a2], EI [auth a3], EK [auth a6], EL [auth bA], EM [auth bA], EN [auth bB], EO [auth bB], EQ [auth b1], ER [auth b2], ET [auth b5], EU [auth b6], EV [auth cA], EW [auth cA], EX [auth cB], EY [auth cB], FB [auth aA], FBA [auth c3], FC [auth aA], FCA [auth c4], FD [auth aB], FDA [auth c5], FE [auth aB], FG [auth a1], FH [auth a2], FI [auth a3], FK [auth a6], FL [auth bA], FM [auth bA], FN [auth bB], FO [auth bB], FQ [auth b1], FR [auth b2], FT [auth b5], FU [auth b6], FV [auth cA], FW [auth cA], FX [auth cB], FY [auth cB], FZ [auth cK], GB [auth aA], GBA [auth c3], GC [auth aA], GCA [auth c4], GD [auth aB], GDA [auth c5], GE [auth aB], GG [auth a1], GH [auth a2], GI [auth a3], GK [auth a6], GL [auth bA], GM [auth bA], GN [auth bB], GO [auth bB], GP [auth bJ], GQ [auth b1], GR [auth b2], GS [auth b3], GT [auth b5], GU [auth b6], GV [auth cA], GW [auth cA], GX [auth cB], GY [auth cB], GZ [auth cL], HB [auth aA], HBA [auth c3], HC [auth aA], HCA [auth c4], HD [auth aB], HDA [auth c5], HE [auth aB], HG [auth a1], HH [auth a2], HI [auth a3], HJ [auth a4], HK [auth a6], HL [auth bA], HM [auth bA], HN [auth bB], HO [auth bB], HP [auth bJ], HQ [auth b1], HR [auth b2], HT [auth b5], HU [auth b6], HV [auth cA], HW [auth cA], HX [auth cB], HY [auth cB], HZ [auth cL], IAA [auth c2], IB [auth aA], IBA [auth c3], IC [auth aA], ICA [auth c4], ID [auth aB], IDA [auth c5], IE [auth aB], IG [auth a1], IH [auth a2], II [auth a3], IK [auth a6], IL [auth bA], IM [auth bA], IN [auth bB], IO [auth bB], IQ [auth b1], IS [auth b4], IT [auth b5], IU [auth b6], IV [auth cA], IW [auth cA], IX [auth cB], IY [auth cB], IZ [auth cL], JAA [auth c2], JB [auth aA], JBA [auth c3], JC [auth aA], JCA [auth c4], JD [auth aB], JDA [auth c5], JE [auth aB], JG [auth a1], JH [auth a2], JJ [auth a5], JK [auth a6], JL [auth bA], JM [auth bA], JN [auth bB], JO [auth bB], JQ [auth b1], JS [auth b4], JT [auth b5], JU [auth b6], JV [auth cA], JW [auth cA], JX [auth cB], KAA [auth c2], KB [auth aA], KBA [auth c3], KC [auth aA], KCA [auth c4], KD [auth aB], KE [auth aB], KF [auth aJ], KG [auth a1], KH [auth a2], KJ [auth a5], KK [auth a6], KL [auth bA], KM [auth bA], KN [auth bB], KO [auth bB], KQ [auth b1], KS [auth b4], KT [auth b5], KU [auth b6], KV [auth cA], KX [auth cB], LAA [auth c2], LB [auth aA], LBA [auth c3], LC [auth aA], LCA [auth c4], LD [auth aB], LE [auth aB], LF [auth aJ], LG [auth a1], LH [auth a2], LJ [auth a5], LK [auth a6], LL [auth bA], LM [auth bA], LN [auth bB], LO [auth bB], LP [auth bK], LQ [auth b1], LR [auth b2], LS [auth b4], LT [auth b5], LU [auth b6], LV [auth cA], LX [auth cB], MAA [auth c2], MB [auth aA], MBA [auth c3], MC [auth aA], MCA [auth c4], MD [auth aB], MDA [auth c5], ME [auth aB], MF [auth aJ], MG [auth a1], MH [auth a2], MI [auth a3], MJ [auth a5], MK [auth a6], ML [auth bA], MM [auth bA], MN [auth bB], MO [auth bB], MQ [auth b1], MS [auth b4], MT [auth b5], MU [auth b6], MV [auth cA], MX [auth cB], MZ [auth cX], NAA [auth c2], NB [auth aA], NBA [auth c3], NC [auth aA], NCA [auth c4], ND [auth aB], NE [auth aB], NG [auth a1], NH [auth a2], NJ [auth a5], NK [auth a6], NL [auth bA], NM [auth bA], NN [auth bB], NO [auth bB], NP [auth bL], NR [auth b3], NS [auth b4], NT [auth b5], NU [auth b6], NV [auth cA], NX [auth cB], OAA [auth c2], OB [auth aA], OBA [auth c3], OC [auth aA], OCA [auth c4], OD [auth aB], OE [auth aB], OG [auth a1], OI [auth a4], OJ [auth a5], OK [auth a6], OL [auth bA], OM [auth bA], ON [auth bB], OO [auth bB], OP [auth bL], OR [auth b3], OS [auth b4], OT [auth b5], OV [auth cA], OX [auth cB], OZ [auth c1], PAA [auth c2], PB [auth aA], PBA [auth c3], PC [auth aA], PD [auth aB], PDA [auth c6], PE [auth aB], PG [auth a1], PI [auth a4], PJ [auth a5], PK [auth a6], PL [auth bA], PM [auth bA], PN [auth bB], PO [auth bB], PP [auth bL], PR [auth b3], PS [auth b4], PT [auth b5], PV [auth cA], PX [auth cB], PZ [auth c1], QAA [auth c2], QB [auth aA], QBA [auth c3], QC [auth aA], QD [auth aB], QDA [auth c6], QE [auth aB], QF [auth aK], QI [auth a4], QJ [auth a5], QK [auth a6], QL [auth bA], QM [auth bA], QN [auth bB], QO [auth bB], QR [auth b3], QS [auth b4], QT [auth b5], QV [auth cA], QX [auth cB], QZ [auth c1], RAA [auth c2], RB [auth aA], RBA [auth c3], RC [auth aA], RD [auth aB], RDA [auth c6], RE [auth aB], RF [auth aL], RH [auth a2], RI [auth a4], RJ [auth a5], RK [auth a6], RL [auth bA], RN [auth bB], RQ [auth b2], RR [auth b3], RS [auth b4], RT [auth b5], RU [auth b6], RV [auth cA], RX [auth cB], RZ [auth c1], SAA [auth c2], SB [auth aA], SBA [auth c3], SC [auth aA], SCA [auth c4], SD [auth aB], SDA [auth c6], SE [auth aB], SF [auth aL], SI [auth a4], SJ [auth a5], SK [auth a6], SL [auth bA], SN [auth bB], SQ [auth b2], SR [auth b3], SS [auth b4], ST [auth b5], SV [auth cA], SX [auth cB], SZ [auth c1], TAA [auth c2], TB [auth aA], TBA [auth c3], TC [auth aA], TD [auth aB], TDA [auth c6], TE [auth aB], TF [auth aL], TH [auth a3], TI [auth a4], TJ [auth a5], TK [auth a6], TL [auth bA], TN [auth bB], TQ [auth b2], TR [auth b3], TS [auth b4], TU [auth cA], TV [auth cA], TW [auth cB], TX [auth cB], TY [auth cF], TZ [auth c1], UAA [auth c2], UB [auth aA], UC [auth aA], UCA [auth c5], UD [auth aB], UDA [auth c6], UH [auth a3], UI [auth a4], UJ [auth a5], UL [auth bA], UN [auth bB], UQ [auth b2], UR [auth b3], US [auth b4], UU [auth cA], UV [auth cA], UW [auth cB], UX [auth cB], UZ [auth c1], VAA [auth c2], VB [auth aA], VCA [auth c5], VD [auth aB], VDA [auth c6], VG [auth a1], VH [auth a3], VI [auth a4], VJ [auth a5], VL [auth bA], VN [auth bB], VP [auth bX], VQ [auth b2], VR [auth b3], VS [auth b4], VT [auth b5], VU [auth cA], VV [auth cA], VW [auth cB], VX [auth cB], VY [auth cF], VZ [auth c1], WAA [auth c2], WB [auth aA], WCA [auth c5], WD [auth aB], WDA [auth c6], WH [auth a3], WI [auth a4], WJ [auth a5], WL [auth bA], WN [auth bB], WQ [auth b2], WR [auth b3], WS [auth b4], WU [auth cA], WV [auth cA], WW [auth cB], WX [auth cB], WZ [auth c1], XAA [auth c2], XB [auth aA], XBA [auth c3], XCA [auth c5], XD [auth aB], XDA [auth c6], XG [auth a2], XH [auth a3], XI [auth a4], XJ [auth a5], XK [auth a6], XL [auth bA], XN [auth bB], XP [auth b1], XQ [auth b2], XR [auth b3], XS [auth b4], XU [auth cA], XV [auth cA], XW [auth cB], XX [auth cB], XZ [auth c1], YAA [auth c2], YB [auth aA], YCA [auth c5], YD [auth aB], YDA [auth c6], YG [auth a2], YH [auth a3], YI [auth a4], YJ [auth a5], YL [auth bA], YN [auth bB], YP [auth b1], YQ [auth b2], YR [auth b3], YT [auth b6], YU [auth cA], YV [auth cA], YW [auth cB], YX [auth cB], YZ [auth c1], ZB [auth aA], ZBA [auth c4], ZCA [auth c5], ZD [auth aB], ZDA [auth c6], ZF [auth aX], ZG [auth a2], ZH [auth a3], ZI [auth a4], ZK [auth bA], ZL [auth bA], ZN [auth bB], ZP [auth b1], ZQ [auth b2], ZR [auth b3], ZT [auth b6], ZU [auth cA], ZV [auth cA], ZW [auth cB], ZX [auth cB], ZZ [auth c1]	CHLOROPHYLL A C55 H72 Mg N4 O5 ATNHDLDRLWWWCB-AENOIHSZSA-M
CL0	CB [auth aA], SU [auth cA], YK [auth bA]	CHLOROPHYLL A ISOMER C55 H72 Mg N4 O5 VIQFHHZSLDFWDU-DVXFRRMCSA-M
LMG	BF [auth aB], QY [auth cB], ZO [auth bB]	1,2-DISTEAROYL-MONOGALACTOSYL-DIGLYCERIDE C45 H86 O10 DCLTVZLYPPIIID-CVELTQQQSA-N
LHG	AN [auth bA], CD [auth aA], DD [auth aA], LZ [auth cX], RW [auth cA], SW [auth cA], UP [auth bX], YF [auth aX], ZM [auth bA]	1,2-DIPALMITOYL-PHOSPHATIDYL-GLYCEROLE C38 H75 O10 P BIABMEZBCHDPBV-MPQUPPDSSA-N
BCR	ABA [auth c2], AD [auth aA], AF [auth aB], AK [auth a5], AT [auth b4], BBA [auth c2], BD [auth aA], CK [auth a6], CT [auth b5], CZ [auth cJ], DBA [auth c3], DK [auth a6], DP [auth bF], DS [auth b3], DZ [auth cJ], EAA [auth c1], EF [auth aF], EJ [auth a4], EP [auth bI], ES [auth b3], EZ [auth cK], FAA [auth c1], FEA [auth c6], FF [auth aF], FJ [auth a4], FP [auth bI], FS [auth b3], GAA [auth c1], GEA [auth c6], GF [auth aF], GJ [auth a4], HAA [auth c2], HF [auth aI], HS [auth b4], IF [auth aI], IJ [auth a5], IP [auth bJ], IR [auth b2], JF [auth aI], JI [auth a3], JP [auth bJ], JR [auth b2], JZ [auth cL], KDA [auth c5], KI [auth a3], KP [auth bJ], KR [auth b2], KY [auth cB], KZ [auth cM], LDA [auth c5], LI [auth a3], LY [auth cB], MP [auth bL], MR [auth b3], MW [auth cA], MY [auth cB], NDA [auth c6], NF [auth aJ], NI [auth a4], NQ [auth b1], NW [auth cA], NY [auth cB], NZ [auth c1], ODA [auth c6], OF [auth aJ], OH [auth a2], OQ [auth b1], OU [auth b6], OW [auth cA], OY [auth cB], PCA [auth c4], PF [auth aK], PH [auth a2], PQ [auth b1], PU [auth b6], PW [auth cA], PY [auth cB], QCA [auth c4], QG [auth a1], QH [auth a2], QP [auth bL], QQ [auth b2], QU [auth b6], QW [auth cA], RCA [auth c4], RG [auth a1], RP [auth bL], SG [auth a1], SH [auth a3], SO [auth bB], TCA [auth c5], TG [auth a1], TM [auth bA], TO [auth bB], TP [auth bM], TT [auth b5], UBA [auth c3], UG [auth a1], UK [auth a6], UM [auth bA], UO [auth bB], UT [auth b5], UY [auth cF], VBA [auth c3], VE [auth aB], VF [auth aL], VK [auth a6], VM [auth bA], VO [auth bB], WBA [auth c3], WE [auth aB], WG [auth a2], WK [auth a6], WM [auth bA], WO [auth bB], WP [auth b1], WT [auth b6], WY [auth cF], XC [auth aA], XE [auth aB], XF [auth aM], XM [auth bA], XO [auth bB], XT [auth b6], XY [auth cF], YBA [auth c4], YC [auth aA], YE [auth aB], YM [auth bA], YO [auth bB], YS [auth b4], YY [auth cI], ZAA [auth c2], ZC [auth aA], ZE [auth aB], ZJ [auth a5], ZS [auth b4], ZY [auth cI]	BETA-CAROTENE C40 H56 OENHQHLEOONYIE-JLTXGRSLSA-N
PQN	JY [auth cB], KW [auth cA], RM [auth bA], RO [auth bB], UE [auth aB], VC [auth aA]	PHYLLOQUINONE C31 H46 O2 MBWXNTAXLNYFJB-NKFFZRIASA-N
SF4	AP [auth bC], BP [auth bC], CF [auth aC], DF [auth aC], LW [auth cA], RY [auth cC], SM [auth bA], SY [auth cC], WC [auth aA]	IRON/SULFUR CLUSTER Fe4 S4 LJBDFODJNLIPKO-UHFFFAOYSA-N
CA	SP [auth bL], UF [auth aL], WF [auth aL]	CALCIUM ION Ca BHPQYMZQTOCNFJ-UHFFFAOYSA-N

Experimental Data & Validation

Experimental Data

• Method: ELECTRON MICROSCOPY
• Resolution: 2.74 Å
• Aggregation State: PARTICLE 
• Reconstruction Method: SINGLE PARTICLE 

EM Software:

Task	Software Package	Version
RECONSTRUCTION	RELION	3
MODEL REFINEMENT	PHENIX	1.13_2998

Structure Validation

Entry History 

Deposition Data

• Released Date: 2020-05-20 
Deposition Author(s): Akita, F., Nagao, R., Kato, K., Shen, J.R., Miyazaki, N.

Revision History  

• Version 1.0: 2020-05-20
  Type: Initial release
  
• Version 1.1: 2020-05-27
  Changes: Database references
• Version 2.0: 2024-10-16
  Changes: Data collection, Database references, Derived calculations, Non-polymer description, Refinement description, Structure summary