Novel mechanism for carbamoyl-phosphate synthetase: A nucleotide switch for functionally equivalent domains

AUTOR(ES)

Kothe, Michael

FONTE

The National Academy of Sciences of the USA

RESUMO

Carbamoyl-phosphate synthetases (CPSs) utilize two molecules of ATP at two internally duplicated domains, B and C. Domains B and C have recently been shown to be structurally [Thoden, J. B., Holden, H. M., Wesenberg, G., Raushel, F. M. & Rayment, I. (1997) Biochemistry 36, 6305–6316] and functionally [Guy, H. I. & Evans, D. R. (1996) J. Biol. Chem. 271, 13762–13769] equivalent. We have carried out a site-directed mutagenic analysis that is consistent with ATP binding to a palmate motif rather than to a Walker A/B motif in domains B and C. To accommodate our present findings, as well as the other recent findings of structural and functional equivalence, we are proposing a novel mechanism for CPS. In this mechanism utilization of ATP bound to domain C is coupled to carbamoyl-phosphate synthesis at domain B via a nucleotide switch, with the energy of ATP hydrolysis at domain C allowing domain B to cycle between two alternative conformations.

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