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Publication Abstract from PubMed

Cyanophycin is a bacterial polymer mainly used for nitrogen storage. It is composed of a peptide backbone of L-aspartate residues with L-arginines attached to their side chains through isopeptide bonds. Cyanophycin is degraded in two steps: Cyanophycinase cleaves the polymer into beta-Asp-Arg dipeptides, which are hydrolyzed into free Asp and Arg by enzymes possessing isoaspartyl dipeptide hydrolase activity. Two unrelated enzymes with this activity, isoaspartyl dipeptidase (IadA) and isoaspartyl aminopeptidase (IaaA) have been shown to degrade beta-Asp-Arg dipeptides, but bacteria which encode cyanophycin-metabolizing genes can lack iaaA and iadA genes. In this study, we investigate a previously uncharacterized enzyme whose gene can cluster with cyanophycin-metabolizing genes. This enzyme, which we name cyanophycin dipeptide hydrolase (CphZ), is specific for dipeptides derived from cyanophycin degradation. Accordingly, a co-complex structure of CphZ and beta-Asp-Arg shows that CphZ, unlike IadA or IaaA, recognizes all portions of its beta-Asp-Arg substrate. Bioinformatic analyses showed that CphZ is found in very many proteobacteria and is homologous to an uncharacterized protein encoded in the "arginine/ornithine transport" (aot) operon of many pseudomonas species, including Pseudomonas aeruginosa. In vitro assays show that AotO is indeed a CphZ, and in cellulo growth experiments show that this enzyme and the aot operon allow P. aeruginosa to take up and use beta-Asp-Arg as a sole carbon and nitrogen source. Together the results establish the novel, highly specific enzyme subfamily of CphZs, suggesting that cyanophycin is potentially used by a much wider range of bacteria than previously appreciated.

Discovery of cyanophycin dipeptide hydrolase enzymes suggests widespread utility of the natural biopolymer cyanophycin.,Sharon I, McKay GA, Nguyen D, Schmeing TM Proc Natl Acad Sci U S A. 2023 Feb 21;120(8):e2216547120. doi: , 10.1073/pnas.2216547120. Epub 2023 Feb 17. PMID:36800389^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.