Crystal structure of a complex formed between proteolytically-generated lactoferrin fragment and proteinase K.Singh, T.P., Sharma, S., Karthikeyan, S., Betzel, C., Bhatia, K.L.
(1998) Proteins 33: 30-38
- PubMed: 9741842
- PubMed Abstract:
- Inhibition of Proteinase K by Methoxysuccinyl-Ala-Ala-Pro-Ala-Chloromethyl Ketone. An X-Ray Study at 2.2-A Resolution
Wolf, W.M.,Bajorath, J.,Muller, A.,Raghunathan, S.,Singh, T.P.,Hinrichs, W.,Saenger, W.
(1991) J.Biol.Chem. 266: 17695
- Synchrotron X-Ray Data Collection and Restrained Least-Squares Refinement of the Crystal Structure of Proteinase K at 1.5 A Resolution
Betzel, C.,Pal, G.P.,Saenger, W.
(1988) Acta Crystallogr.,Sect.B 44: 163
Lactoferrin is an iron binding glycoprotein with a molecular weight of 80 kDa. The molecule is divided into two lobes representing the N-terminal and C-terminal halves of the polypeptide chain, each containing an iron binding site. The serine protein ...
Lactoferrin is an iron binding glycoprotein with a molecular weight of 80 kDa. The molecule is divided into two lobes representing the N-terminal and C-terminal halves of the polypeptide chain, each containing an iron binding site. The serine proteinases such as trypsin, chymotrypsin, and pepsin hydrolyze lactoferrin into two unequal halves while proteinase K divides this protein into two equal halves. In the first step of hydrolysis by proteinase K, the C- and N-lobes, each having a molecular weight of approximately 40 kDa, are generated. In the next step, the lobes are further hydrolyzed into small molecular weight peptides. The proteinase K isolated from the hydrolyzed product does not show enzymatic activity suggesting that the enzyme is inhibited. Furthermore, the hydrolysis experiments on N-lobe and C-lobe showed that the inhibitory fragment came from the C-lobe. The purified lactoferrin fragment was found to be a decapeptide with an amino acid sequence of H2N-Val-Ala-Gln-Gly-Ala-Ala-Gly-Leu-Ala-COOH. The complex formed between proteinase K and lactoferrin fragment was crystallized by microdialysis. The crystals belonged to the monoclinic space group P2(1) with cell dimensions a = 44.4 A, b = 38.6 A, c = 79.2 A, beta = 105.8 degrees and Z = 2. The crystal structure has been determined at 2.4 A resolution. It has been refined to an R factor of 0.163 for 9044 reflections. The Lf-fragment forms several intermolecular interactions with proteinase K. The Ser-224 Ogamma and His-57 N epsilon2 move away to a distance of 3.68 A in the complex. In the crystal structure, Gln-3I (I indicates inhibitor i.e., lactoferrin fragment) is involved in a direct intermolecular interaction with a symmetry related proteinase K molecule through a strong hydrogen bond with Asp-254. The mode of intermolecular interactions in the complex conformational features of the enzyme and placement of the fragment with respect to the enzyme resemble with the molecular complex of proteinase K with its natural inhibitor PKI3 from wheat.
Department of Biophysics, All India Institute of Medical Sciences, New Delhi. firstname.lastname@example.org