UMMS Affiliation

Division of Digestive Diseases and Nutrition

Date

4-20-2004

Document Type

Article

Subjects

Alternative Splicing; Animals; COS Cells; Catalysis; Cell Line; Cercopithecus aethiops; Dimerization; Electrophoretic Mobility Shift Assay; Enzyme Activation; Histidine; Histidine Decarboxylase; inhibitors; Isoenzymes; Methylhistidines; Oligonucleotides; Peptides; Protein Structure, Tertiary; Pyridoxal Phosphate; Rats; Recombinant Proteins; Substrate Specificity

Disciplines

Biochemistry, Biophysics, and Structural Biology | Molecular, Genetic, and Biochemical Nutrition

Abstract

Full-length rat HDC (L-histidine decarboxylase) translated in reticulocyte cell lysate reactions is inactive, whereas C-terminally truncated isoforms are capable of histamine biosynthesis. C-terminal processing of the approximately 74 kDa full-length protein occurs naturally in vivo, with the production of multiple truncated isoforms. The minimal C-terminal truncation required for the acquisition of catalytic competence has yet to be defined, however, and it remains unclear as to why truncation is needed. Here we show that approximately 74 kDa HDC monomers can form dimers, which is the conformation in which the enzyme is thought to be catalytically active. Nevertheless, the resulting dimer is unable to establish pyridoxal phosphate-dependent interactions with an L-histidine substrate analogue. Protein sequences localized to between amino acids 617 and 633 specifically mediate this inhibition. Removing this region or replacing the entire C-terminus with non-HDC protein sequences permitted interactions with the substrate analogue to be re-established. This corresponded exactly with the acquisition of catalytic competence, and the ability to decarboxylate natural L-histidine substrate. These studies suggested that the approximately 74 kDa full-length isoform is deficient in substrate binding, and demonstrated that C-terminally truncated isoforms with molecular masses between approximately 70 kDa and approximately 58 kDa have gradually increasing specific activities. The physiological relevance of our results is discussed in the context of differential expression of HDC isoforms in vivo.

Rights and Permissions

Citation: Biochem J. 2004 Aug 1;381(Pt 3):769-78. Link to article on publisher's site

DOI of Published Version

10.1042/BJ20031553

Related Resources

Link to article in PubMed

Journal Title

The Biochemical journal

PubMed ID

15089748

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