Analysis of suppressor mutation reveals long distance interactions in the bc(1) complex of Saccharomyces cerevisiae

Four totally conserved glycines are involved in the packing of the two cyto chrome b hemes, b(L) and b(H), of the bc(1) complex. The conserved glycine 131 is involved in the packing of heme b(L) and is separated by only 3 Angs trom from this heme in the bc(1) complex structure. The cytochrome b respir atory deficient mutant G131S is affected in the assembly of the bc(1) compl ex. Am intragenic suppressor mutation was obtained at position 260, in the ef loop, where a glycine was replaced by an alanine. This respiratory compe tent revertant exhibited a low be, complex activity and was affected in the electron transfer at the Q(P) site. The k(min) for the substrate DBH2 was diminished by an order of magnitude and EPR spectra showed a partially empt y Q(P) site. However, the binding of the Q(P) site inhibitors stigmatellin and myxothiazol remained unchanged in the suppressor strain. Optical spectr oscopy revealed that heme b(L) is red shifted by 0.8 nm and that the E-m of heme b(L) was slightly increased (+20 mV) in the revertant strain as compa red to wild type strain values. Addition of a methyl group at position 260 is thus sufficient to allow the assembly of the bc(1) complex and the inser tion of heme bL despite the presence of the serine at position 131. Surpris ingly, reversion at position 260 was located 13 Angstrom away from the orig inal mutation and revealed a long distance interaction in the yeast bc(1) c omplex. (C) 2001 Elsevier Science B.V. All rights reserved.