1b0c
From Proteopedia
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EVIDENCE OF A COMMON DECAMER IN THREE CRYSTAL STRUCTURES OF BPTI, CRYSTALLIZED FROM THIOCYANATE, CHLORIDE OR SULFATE
Overview
Bovine pancreatic trypsin inhibitor (BPTI) crystallizes under acidic pH, conditions in the presence of thiocyanate, chloride and sulfate ions, yielding three different polymorphs in P2(1), P6(4)22 and P6(3)22 space, groups, respectively. In all three crystal forms, the same decamer is, found in the packing (ten BPTI molecules organized through two, perpendicular 2-fold and 5-fold axes as a well-defined and compact object), in contrast to the monomeric crystal forms observed at basic pH, conditions. The crystallization of BPTI under acidic conditions (pH 4.5), was investigated by small angle X-ray scattering with both under- and, supersaturated BPTI solutions. Data showed the oligomerization of BPTI, molecules under all investigated conditions. Accordingly, various mixtures, of discrete oligomers (n=1 to 10) were considered. Calculated scattering, curves were obtained using models based on the crystallographic, structures, and the experimental patterns were analyzed as a linear, combination of the model curves using a non-linear curve fitting, procedure. The results, confirmed by gel filtration experiments, unambiguously demonstrate the co-existence of two different BPTI particles, in solution: a monomer and a decamer, with no evidence of any other, intermediates. Moreover, using both approaches, the fraction of decamers, was found to increase with increasing salt concentration, even beyond the, solubility curve. We therefore propose that at acidic pH, BPTI, crystallizes following a two step process: decamers are first built in, under- and supersaturated solutions, upon which crystal growth proceeds by, decamer stacking. Indeed, those BPTI crystals should best be described as, "BPTI decamer" crystals.
About this Structure
1B0C is a Single protein structure of sequence from Bos taurus. Full crystallographic information is available from OCA.
Reference
The BPTI decamer observed in acidic pH crystal forms pre-exists as a stable species in solution., Hamiaux C, Perez J, Prange T, Veesler S, Ries-Kautt M, Vachette P, J Mol Biol. 2000 Mar 31;297(3):697-712. PMID:10731422
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