STRUCTURAL AND FUNCTIONAL CONSEQUENCES OF SUBSTITUTIONS AT THE PRO108-ARG14 HYDROGEN-BOND IN BOVINE ADRENODOXIN

Elimination of Pro108 in bovine adrenodoxin is known to result in the formation of a misfolded protein that is not able to incorporate a [2F e-2S] cluster and rapidly degrades upon expression in E. coli, However , no experimental explanation for this phenomenon has been demonstrate d so far. Using the recently obtained 3D structure of the truncated mu tant Adx(4-108) we have studied the reasons of the protein stabilizati on by the proline residue by means of site-directed mutagenesis, Two m ain results have been obtained: (i) the conserved hydrogen bond Pro108 -Arg14, that connects different structural domains of Adx, contributes 6 kJ/mol into the protein stability and (ii) the presence of proline at position 108 provides a low conformational entropy of the unfolded state, supporting a gain in the Gibbs energy of 5.4 kJ/mol at 37 degre es C. (C) 1998 Academic Press.