The crystal and molecular structure of the third domain of silver pheasant ovomucoid (OMSVP3)

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Abstract
OMSVP3 and OMTKY3 (third domains of silver pheasant and turkey ovomucoid inhibitor) are Kazal‐type serine proteinase inhibitors. They have been isomorphously crystallized in the monoclinic space group C2 with cell dimensions of a= 4.429 nm, b= 2.115 nm, c= 4.405 nm, β= 107°. The asymmetric unit contains one molecule corresponding to an extremely low volume per unit molecular mass of 0.0017 nm3/Da. Data collection was only possible for the OMSVP3 crystals. Orientation and position of the OMSVP3 molecules in the monoclinic unit cells were determined using Patterson search methods and the known structure of the third domain of Japanese quail ovomucoid (OMJPQ3) [Papamokos, E., Weber, E., Bode, W., Huber, R., Empie, M. W., Kato, I. and Laskowski, M., Jr (1982) J. Mol. Biol. 158, 515–537]. The OMSVP3 structure has been refined by restrained crystallographic refinement yielding a final R value of 0.199 for data to 0.15 nm resolution. Conformation and hydrogen‐bonding pattern of OMSVP3 and OMJPQ3 are very similar. Large deviations occur at the NH2 terminus owing to different crystal packing, and at the C terminus of the central helix, representing an intrinsic property and resulting from amino acid substitutions far away from this site. The deviation of OMSVP3 from OMTKY3 complexed with the Streptomyces griseus protease B is very small [Fujinaga, M., Read, R. J., Sielecki, A., Ardelt, W., Laskowski, M., Jr and James, M. N. G. (1982)Proc. Natl Acad. Sci. USA, 79, 4868–4872].