Role of specific lysine residues in binding cytochrome c2 to the Rhodobacter sphaeroides reaction center in optimal orientation for rapid electron transfer

Abstract

The role of specific lysine residues in facilitating electron transfer from Rhodobacter sphaeroides cytochrome c2 to the Rb. sphaeroides reaction center was studied by using six cytochrome c2 derivatives each labeled at a single lysine residue with a carboxydinitrophenyl group. The reaction of native cytochrome c2 at low ionic strength has a fast phase with a half-time of 0.6 microseconds that has been assigned to the reaction of bound cytochrome c2 [Overfield, R.E., Wraight, C.A., & DeVault, D. (1979) FEBS Lett. 105, 137]. Modification of lysine-55 did not affect the half-time of this phase but decreased the apparent binding constant by a factor of 2. The derivatives modified at lysines-10, -88, -95, -97, -99, -105, and -106 surrounding the heme crevice did not show any detectable fast phase but only slow second-order phases due to the reaction of solution cytochrome c2. These lysines thus appear to be involved in binding cytochrome c2 to the reaction center in an optimal orientation for electron transfer. The involvement of lysines-95 and -97 is especially significant, since they are located in an extra loop comprising residues 89-98 that is not present in eukaryotic cytochrome c. The reactions of horse cytochrome c derivatives modified at single lysine amino groups with trifluoroacetyl or [(trifluoromethyl)phenyl]carbamoyl were also studied. The derivatives modified at lysines-22, -55, -88, and -99 far removed from the heme crevice had nearly the same half-times for the fast phase as native cytochrome c, 6 microseconds.(ABSTRACT TRUNCATED AT 250 WORDS)

Transition state and encounter complex for fast association of cytochrome c 2 with bacterial reaction center

“…Changes to charge-surface groups near the binding interface by using chemical modification (22,23) and site-directed mutagenesis (13,24,25) were shown to change the association rate. The role of electrostatic interactions in protein association was demonstrated by modeling studies (26)(27)(28)(29)(30).…”

Kinetics of photo-induced electron transfer from high-potential iron-sulfur protein to the photosynthetic reaction center of the purple phototroph Rhodoferax fermentans.

“…On the basis of the HiPIP concentration dependence of the amplitude of the fast reaction, the dissociation constant for this HiPIP-RC complex can be estimated as being -2.5 ,M. The latter value is to be compared with the value of 0.1-10 ,uM for the corresponding cytochrome c2-RC complex in Rb. sphaeroides (19)(20)(21)43). The saturation behavior of the second-order plot (Fig.…”

Spectroscopic and Electrochemical Studies on Active-site Transitions of the Type 1 Copper Protein Pseudoazurin from Achromobacter cycloclastes

“…This amino acid residue is located in a similar position to Tyr-83 in plastocyanin, which is in the middle of the remote acidic patch of the protein. In studies on cytochrome c 2 from Rhodobacter spheroides, specific lysine residues have been proposed as a part of the binding site, their role being to create an optional orientation for electron transfer (45), and a similar role for lysine residues in pseudoazurin is also possible.…”