Premium
Role of the surface charges D72 and K8 in the function and structural stability of the cytochrome c 6 from Nostoc sp. PCC 7119
Author(s) -
Lange Christian,
Luque Irene,
Hervás Manuel,
RuizSanz Javier,
Mateo Pedro L.,
De la Rosa Miguel A.
Publication year - 2005
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2005.04747.x
Subject(s) - chemistry , asparagine , cytochrome , photosystem i , mutant , photosystem ii , crystallography , amino acid , biochemistry , photosynthesis , enzyme , gene
We investigated the role of electrostatic charges at positions D72 and K8 in the function and structural stability of cytochrome c 6 from Nostoc sp. PCC 7119 (cyt c 6 ). A series of mutant forms was generated to span the possible combinations of charge neutralization (by mutation to alanine) and charge inversion (by mutation to lysine and aspartate, respectively) in these positions. All forms of cyt c 6 were functionally characterized by laser flash absorption spectroscopy, and their stability was probed by urea‐induced folding equilibrium relaxation experiments and differential scanning calorimetry. Neutralization or inversion of the positive charge at position K8 reduced the efficiency of electron transfer to photosystem I. This effect could not be reversed by compensating for the change in global charge that had been introduced by the mutation, indicating a specific role for K8 in the formation of the electron transfer complex between cyt c 6 and photosystem I. Replacement of D72 by asparagine or lysine increased the efficiency of electron transfer to photosystem I, but destabilized the protein. D72 apparently participates in electrostatic interactions that stabilize the structure of cyt c 6 . The destabilizing effect was reduced when aspartate was replaced by the small amino acid alanine. Complementing the mutation D72A with a charge neutralization or inversion at position K8 led to mutant forms of cyt c 6 that were more stable than the wild‐type under all tested conditions.