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PCC6803 Cyanophycinase S132DAP covalently bound to cyanophycin dimer
Structural highlights
FunctionCPHB_SYNY3 Exopeptidase that catalyzes the hydrolytic cleavage of multi-L-arginyl-poly-L-aspartic acid (cyanophycin; a water-insoluble reserve polymer) into aspartate-arginine dipeptides. Publication Abstract from PubMedBACKGROUND: Cyanophycinases are serine protease family enzymes which are required for the metabolism of cyanophycin, the natural polymer multi-L-arginyl-poly(L-aspartic acid). Cyanophycinases degrade cyanophycin to beta-Asp-Arg dipeptides, which enables use of this important store of fixed nitrogen. METHODS: We used genetic code expansion to incorporate diaminopropionic acid into cyanophycinase in place of the active site serine, and determined a high-resolution structure of the covalent acyl-enzyme intermediate resulting from attack of cyanophycinase on a short cyanophycin segment. RESULTS: The structure indicates that cyanophycin dipeptide residues P1 and P1' bind shallow pockets adjacent to the catalytic residues. We observe many cyanophycinase - P1 dipeptide interactions in the co-complex structure. Calorimetry measurements show that at least two cyanophycin dipeptides are needed for high affinity binding to cyanophycinase. We also characterized a putative cyanophycinase which we found to be structurally very similar but that shows no activity and could not be activated by mutation of its active site. GENERAL SIGNIFICANCE: Despite its peptidic structure, cyanophycin is resistant to degradation by peptidases and other proteases. Our results help show how cyanophycinase can specifically bind and degrade this important polymer. The structure of cyanophycinase in complex with a cyanophycin degradation intermediate.,Sharon I, Grogg M, Hilvert D, Schmeing TM Biochim Biophys Acta Gen Subj. 2022 Jul 26;1866(11):130217. doi:, 10.1016/j.bbagen.2022.130217. PMID:35905922[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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