SEQUENTIAL H-1 AND N-15 NUCLEAR-MAGNETIC-RESONANCE ASSIGNMENTS AND SECONDARY STRUCTURE OF THE N-TERMINAL LIPOYL DOMAIN OF THE DIHYDROLIPOYLTRANSACETYLASE COMPONENT OF THE PYRUVATE-DEHYDROGENASE COMPLEX FROM AZOTOBACTER-VINELANDII
A. Berg et al., SEQUENTIAL H-1 AND N-15 NUCLEAR-MAGNETIC-RESONANCE ASSIGNMENTS AND SECONDARY STRUCTURE OF THE N-TERMINAL LIPOYL DOMAIN OF THE DIHYDROLIPOYLTRANSACETYLASE COMPONENT OF THE PYRUVATE-DEHYDROGENASE COMPLEX FROM AZOTOBACTER-VINELANDII, European journal of biochemistry, 221(1), 1994, pp. 87-100
The N-terminal lipoyl domain (79 residues) of the transacetylase compo
nent of the pyruvate dehydrogenase complex from Azotobacter vinelandii
has been sub-cloned and produced in Escherichia coli. Over-expression
exceeds the capacity of E. coli cells to lipoylate all expressed lipo
yl domain, but addition of lipoic acid to the growth medium results in
expression of fully lipolylated domain. A two-dimensional homo- and h
eteronuclear NMR study of the lipoyl domain has resulted in sequential
H-1 and N-15 resonance assignments of the unlipoylated form of the pr
otein. Small differences in chemical shift values for protons of resid
ues in the vicinity of the lipoyl-lysine residue are observed for the
lipoylated form of the domain, suggesting that the conformation of the
lipoyl domain is not altered significantly by the coupled cofactor. F
rom nuclear Overhauser effects, backbone coupling constants and slowly
exchanging amide protons, two antiparallel beta-sheets, each containi
ng four strands, were identified. The lipoyl-lysine residue is exposed
to the solvent and located in a type-I turn between two strands. The
N- and C-terminal residues of the folded chain are close together in t
he other sheet. Preliminary data on the relative three-dimensional ori
entation of the two beta-sheets are presented. Comparison with the sol
ution structure of the lipoyl domain of the Bacillus stearothermophilu
s pyruvate dehydrogenase complex shows resemblance to a large extent,
despite the sequence identity of 31%.