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Updated: Jun 16, 2026

An Integrated Approach for Microprotein Identification and Sequence Analysis
Published on: July 12, 2022
Holocarboxylase synthetase: correlation of protein localisation with biological function
L M Bailey1, J C Wallace, S W Polyak
1School of Molecular and Biomedical Science, University of Adelaide, Adelaide, South Australia 5005, Australia.
Abstract:
Holocarboxylase synthetase (HCS) governs the cellular fate of the essential micronutrient biotin (Vitamin H or B7). HCS is responsible for attaching biotin onto the biotin-dependent enzymes that reside in the cytoplasm and mitochondria. Evidence for an alternative role, viz the regulation of gene expression, has also been reported. Recent immunohistochemical studies reported HCS is primarily nuclear, inconsistent with the location of HCS activity. Improved understanding of biotin biology demands greater knowledge about HCS. Here, we investigated the localisation of HCS and its isoforms. Three variants were observed that differ at the N-terminus. All HCS isoforms were predominantly non-nuclear, consistent with the distribution of biotin protein ligase activity. Unlike the longer constructs, the Met(58) isoform was also detected in the nucleus--a novel observation suggesting shuttling activity between nucleus and cytoplasm. We resolved that the previous controversies in the literature are due to specificity and detection limitations that arise when using partially purified antibodies.
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