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B6db references: 28042035

type Journal Article
authors Tassoni R, van der Aart LT, Ubbink M, van Wezel GP, Pannu NS
title Structural and functional characterization of the alanine racemase from Streptomyces coelicolor A3(2)
journal Biochem Biophys Res Commun
sel selected
ui 28042035
year (2017)
volume 483
number 1
pages 122-128
keywords Actinobacteria; Alanine racemase; Antibiotic resistance; Peptidoglycan; X-ray crystallography
abstract The conversion of l-alanine (L-Ala) into d-alanine (D-Ala) in bacteria is performed by pyridoxal phosphate-dependent enzymes called alanine racemases. D-Ala is an essential component of the bacterial peptidoglycan and hence required for survival. The Gram-positive bacterium Streptomyces coelicolor has at least one alanine racemase encoded by alr. Here, we describe an alr deletion mutant of S. coelicolor which depends on D-Ala for growth and shows increased sensitivity to the antibiotic d-cycloserine (DCS). The crystal structure of the alanine racemase (Alr) was solved with and without the inhibitors DCS or propionate, at 1.64 and 1.51 resolution, respectively. The crystal structures revealed that Alr is a homodimer with residues from both monomers contributing to the active site. The dimeric state of the enzyme in solution was confirmed by gel filtration chromatography, with and without L-Ala or d-cycloserine. The activity of the enzyme was 66 3 U mg-1 for the racemization of L- to D-Ala, and 104 7 U mg-1 for the opposite direction. Comparison of Alr from S. coelicolor with orthologous enzymes from other bacteria, including the closely related d-cycloserine-resistant Alr from S. lavendulae, strongly suggests that structural features such as the hinge angle or the surface area between the monomers do not contribute to d-cycloserine resistance, and the molecular basis for resistance therefore remains elusive.
last changed 2017/07/12 13:22

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