4o4o

Crystal structure of phycobiliprotein lyase CpcT

spinqualitylabelsall models 4o4o, resolution 1.95Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Structural highlights 4o4o is a 2 chain structure. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance. Ligands: MG NonStd Res: MSE Related: 4o4s Resources: FirstGlance, OCA, RCSB, PDBsum Function [CPCT_NOSS1] Catalyzes the site-selective attachment of phycocyanobilin (PCB) to 'Cys-154' of C-phycocyanin subunit beta (CpcB) and to 'Cys-153' of phycoerythrocyanin subunit beta (PecB). Does not have chromophore lyase activity for ApcA1, ApcA2, ApcB, ApcD, ApcF or PecA. Publication Abstract from PubMed Pigmentation of light-harvesting phycobiliproteins of cyanobacteria requires covalent attachment of open-chain tetrapyrroles, bilins, to the apoproteins. Thioether formation via addition of a cysteine residue to the 3-ethylidene substituent of bilins is mediated by lyases. T-type lyases are responsible for attachment to Cys155 of phycobiliprotein beta-subunits. We present crystal structures of CpcT (All5339) from Nostoc sp. PCC7120 and its complex with phycocyanobilin, at 1.95 and 2.50 Angstrom resolution, respectively. CpcT forms a dimer and adopts a calyx-shaped beta-barrel fold. While the overall structure of CpcT is largely retained upon chromophore binding, arginine residues at the opening of the binding pocket undergo major rotameric rearrangements anchoring the propionate groups of phycocyanobilin. Based on the structure and mutational analysis, a reaction mechanism is proposed that accounts for chromophore stabilization, and regio- and stereospecificity of the addition reaction. At the dimer interface, a loop extending from one subunit partially shields the opening of the phycocyanobilin binding pocket in the other subunit. Deletion of the loop or disruptions of the dimer interface significantly reduce CpcT lyase activity, suggesting functional relevance of the dimer. Dimerization is further enhanced by chromophore binding. The chromophore is largely buried in the dimer but in the monomer the 3-ethylidene group is accessible for the apo-phycobiliprotein, preferentially from the chromophore alpha-side. Asp163 and Tyr65 at the beta- and alpha-face near the E-configured ethylidene group, respectively, support the acid-catalyzed nucleophilic Michael addition of cysteine-155 of the apoprotein to an N-acylimmonium intermediate proposed by K. Grubmayr and U.G. Wagner (Monatsh. Chem. 119, 965, 1988). Structure and Mechanism of the Phycobiliprotein Lyase CpcT.,Zhou W, Ding WL, Zeng XL, Dong LL, Zhao B, Zhou M, Scheer H, Zhao KH, Yang X J Biol Chem. 2014 Jul 29. pii: jbc.M114.586743. PMID:25074932 From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.

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