PMID:19053264

Citation	Abresch, EC, Paddock, ML, Villalobos, M, Chang, C and Okamura, MY (2008) Interaction between cytochrome c2 and the photosynthetic reaction center from Rhodobacter sphaeroides: role of interprotein hydrogen bonds in binding and electron transfer. Biochemistry 47:13318-25
Abstract	The role of short-range hydrogen bond interactions at the interface between electron transfer proteins cytochrome c(2) (cyt) and the reaction center (RC) from Rhodobacter sphaeroides was studied by mutation (to Ala) of RC residues Asn M187, Asn M188, and Gln L258 which form interprotein hydrogen bonds to cyt in the cyt-RC complex. The largest decrease in binding constant K(A) (8-fold) for a single mutation was observed for Asn M187, which forms an intraprotein hydrogen bond to the key residue Tyr L162 in the center of the contact region with a low solvent accessibility. Interaction between Asn M187 and Tyr L162 was also implicated in binding by double mutation of the two residues. The hydrogen bond mutations did not significantly change the second-order rate constant, k(2), indicating the mutations did not change the association rate for formation of the cyt-RC complex but increased the dissociation rate. The first-order electron transfer rate, k(e), for the cyt-RC complex was reduced by a factor of up to 4 (for Asn M187). The changes in k(e) were correlated with the changes in binding affinity but were not accompanied by increases in activation energy. We conclude that short-range hydrogen bond interactions contribute to the close packing of residues in the central contact region between the cyt and RC near Asn M187 and Tyr L162. The close packing contributes to fast electron transfer by increasing the rate of electronic coupling and contributes to the binding energy holding the cyt in position for times sufficient for electron transfer to occur.
Links	PubMed PMC2615004 Online version:10.1021/bi801675a
Keywords	Amino Acid Substitution/genetics; Bacterial Proteins/chemistry; Bacterial Proteins/genetics; Bacterial Proteins/metabolism; Crystallography, X-Ray; Cytochromes c2/chemistry; Cytochromes c2/genetics; Cytochromes c2/metabolism; Electron Transport/genetics; Hydrogen Bonding; Mutagenesis, Site-Directed; Photosynthetic Reaction Center Complex Proteins/chemistry; Photosynthetic Reaction Center Complex Proteins/genetics; Photosynthetic Reaction Center Complex Proteins/metabolism; Protein Binding/genetics; Protein Interaction Mapping; Protein Structure, Secondary/genetics; Rhodobacter sphaeroides/enzymology; Rhodobacter sphaeroides/genetics; Rhodobacter sphaeroides/metabolism
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
RHORT:CYC2	involved_in	GO:0009767: photosynthetic electron transport chain	ECO:0000314: direct assay evidence used in manual assertion		P		Seeded From UniProt	complete
RHORT:CYC2		GO:0009767: photosynthetic electron transport chain	ECO:0000314:		P		Figure 7 and Figure 2 show electron transfer rate from Cyt c2 to the reaction center	complete CACAO 3471

References

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