Monomeric Form of Peptidylarginine Deiminase Type I Revealed by X-ray Crystallography and Small-Angle X-ray Scattering.

Peptidylarginine deiminase EC 3.5.3.15) is a post-translational modification enzyme that catalyzes the conversion of arginine in protein molecules to a citrulline residue in a Ca(2+)-dependent manner. In this study, we determined the structure of an active form of human crystallized in the presence of Ca(2+) at 3.2-Å resolution. Although human and isozymes were previously reported to form a head-to-tail homodimer, it is still unknown whether this quaternary structure is common to other isozymes. The asymmetric unit of the crystal contained two duanyu15631 molecules; however, the head-to-tail dimeric form was not found. Small-angle X-ray scattering analyses revealed duanyu15631 to be a monomer in solution, while was dimerized with a structure similar to duanyu15632 and duanyu15631 was apparently different from the crystal structures of duanyu15632 and with an elongated N-terminal loop that appears to prevent the formation of the homodimer. Of interest, the N-terminal loop occupied the substrate binding site of the adjacent duanyu15631 molecules in the crystal. Deimination of S100A3 peptides in vitro implied that duanyu1563 isozymes recognize the quaternary structure of S100A3. The substrate-accessible monomeric structure brought about by the extension of its N terminus may partly account for the highest tolerant substrate recognition of This is the first ever report on the molecular structure of duanyu15631 demonstrating the unique monomeric form of the duanyu1563 isozyme.

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