Function of a conserved loop of the beta-domain, not involved in thiamin diphosphate binding, in catalysis and substrate activation in yeast pyruvate decarboxylase

TitleFunction of a conserved loop of the beta-domain, not involved in thiamin diphosphate binding, in catalysis and substrate activation in yeast pyruvate decarboxylase
Publication TypeJournal Article
Year of Publication2006
AuthorsJoseph, E, Wei W, Tittmann K, Jordan F
JournalBiochemistry
Volume45
Pagination13517-13527
Date PublishedNov
Type of ArticleArticle
ISBN Number0006-2960
Accession Numberhttp://apps.isiknowledge.com/InboundService.do?Func=Frame&product=WOS&action=retrieve&SrcApp=EndNote&Init=Yes&SrcAuth=ResearchSoft&mode=FullRecord&UT=000241808300012
KeywordsCYSTEINES, ENZYME, INFORMATION-TRANSFER, MECHANISM, RESOLUTION, SACCHAROMYCES-CEREVISIAE, SITE-DIRECTED MUTAGENESIS, STATE
Abstract

The X-ray crystal structure of pyruvamide-activated yeast pyruvate decarboxylase (YPDC) revealed a flexible loop spanning residues 290 to 304 on the beta-domain of the enzyme, not seen in the absence of pyruvamide, a substrate activator surrogate. Site-directed mutagenesis studies revealed that residues on the loop affect the activity, with some residues reducing k(cat)/K-m by at least 1000-fold. In the pyruvamide-activated form, the loop located on the, domain can transfer information to the active center thiamin diphosphate (ThDP) located at the interface of the alpha and gamma domains. The sigmoidal v(0)-[S] curve with wild-type YPDC attributed to substrate activation is modulated for most variants, but is not abolished. Pre-steady-state stopped-flow studies for product formation on these loop variants provided evidence for three enzyme conformations connected by two transitions, as already noted for the wild-type YPDC at pH 5.0 [Sergienko, E. A., and Jordan, F. ( 2002) Biochemistry 41, 3952-3967]. H-1 NMR analysis of the intermediate distribution resulting from acid quench [Tittmann et al. ( 2003) Biochemistry 42, 78857891] with all YPDC variants indicated that product release is rate limiting in the steady state. Apparently, the loop is not solely responsible for the substrate activation behavior, rather it may affect the behavior of residue C221 identified as the trigger for substrate activation. The most important function of the loop is to control the conformational equilibrium between the "open" and "closed" conformations of the enzyme identified in the pyruvamide-activated structure

URLhttp://apps.isiknowledge.com/InboundService.do?Func=Frame&product=WOS&action=retrieve&SrcApp=EndNote&Init=Yes&SrcAuth=ResearchSoft&mode=FullRecord&UT=000241808300012
Alternate JournalBiochemistry