Complex formation by bovine trypsin and a tetrapeptide (Leu-Arg-Pro-Gly-NH2): X-ray structure analysis of the complex in the orthorhombic crystal form with low molecular packing density.

The title tetrapeptide, Leu-Arg-Pro-Gly-NH2, forms a complex with trypsin in a novel orthorhombic crystal form with low molecular packing density. The complex formation was directly evidenced by X-ray crystallography. The crystal structure at 1.8 A resolution was refined to an R-factor of 20.5% for 13,923 reflection data, which were measured with synchrotron radiation. The tetrapeptide is bound to trypsin at the active site, and the binding mode is very similar to that of a bovine pancreatic trypsin inhibitor (BPTI):trypsin complex. The tetrapeptide:trypsin complex is the first observation that a peptide forms a stable complex with trypsin.