AUTHOR=Zeng Qi , Yang Qi , Jia Jia , Bi Hongkai 

TITLE=A Moraxella Virulence Factor Catalyzes an Essential Esterase Reaction of Biotin Biosynthesis

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.00148

DOI=10.3389/fmicb.2020.00148

ISSN=1664-302X

ABSTRACT=<p>Pimeloyl-acyl carrier protein (ACP) methyl ester esterase catalyzes the last biosynthetic step of the pimelate moiety of biotin, a key intermediate in biotin biosynthesis. The paradigm pimeloyl-ACP methyl ester esterase is the BioH protein of <italic>Escherichia coli</italic> that hydrolyses the ester bond of pimeloyl-ACP methyl ester. Biotin synthesis in <italic>E. coli</italic> also requires the function of the malonyl-ACP methyltransferase gene (<italic>bioC</italic>) to employ a methylation strategy to allow elongation of a temporarily disguised malonate moiety to a pimelate moiety by the fatty acid synthetic enzymes. However, bioinformatics analyses of the extant bacterial genomes showed that <italic>bioH</italic> is absent in many <italic>bioC</italic>-containing bacteria. The genome of the Gram-negative bacterium, <italic>Moraxella catarrhalis</italic> lacks a gene encoding a homolog of any of the six known pimeloyl-ACP methyl ester esterase isozymes suggesting that this organism encodes a novel pimeloyl-ACP methyl ester esterase isoform. We report that this is the case. The gene encoding the new isoform, called <italic>btsA</italic>, was isolated by complementation of an <italic>E. coli bioH</italic> deletion strain. The requirement of BtsA for the biotin biosynthesis in <italic>M. catarrhalis</italic> was confirmed by a biotin auxotrophic phenotype caused by deletion of <italic>btsA in vivo</italic> and a reconstituted <italic>in vitro</italic> desthiobiotin synthesis system. Purified BtsA was shown to cleave the physiological substrate pimeloyl-ACP methyl ester to pimeloyl-ACP by use of a Ser117-His254-Asp287 catalytic triad. The lack of sequence alignment with other isozymes together with phylogenetic analyses revealed BtsA as a new class of pimeloyl-ACP methyl ester esterase. The involvement of BtsA in <italic>M. catarrhalis</italic> virulence was confirmed by the defect of bacterial invasion to lung epithelial cells and survival within macrophages in the Δ<italic>btsA</italic> strains. Identification of the new esterase gene <italic>btsA</italic> exclusive in <italic>Moraxella</italic> species that links biotin biosynthesis to bacterial virulence, can reveal a new valuable target for development of drugs against <italic>M. catarrhalis</italic>.</p>