Department of Biophysics, All India Institute of Medical Sciences, New Delhi-110029.
○Rafia Mir Sujata Sharma Nagendra Singh Mau Sinha A. S. Ethayathulla R. Prem kumar Punit Kaur Tej. P. Singh
Lactoferrin is an iron-binding protein with a bilobed structure. Each lobe contains a high affinity binding site for a single Fe3+ ion and an associated Co32- ion. In addition to it, lactoferrin is involved in various other roles. In order to identify new binding sites in lactoferrin, it is desirable to focus lobe-wise. Therefore, lactoferrin was hydrolyzed with proteinase K to generate N- and C- lobes. Lobes were purified and the purified C-lobe was used for determining the sugar binding sites on the C-lobe. It was co-crystallized with sugars, mannose, galactose, xylose, lactose, glucose, N-acetylglucosamine and sucrose, and their crystal structures were determined. A unique sugar binding site was identified to which different types of sugars bound repeatedly. Although the binding site is a shallow structure, it has preferred residues for interactions. The residues Glu 659, Tyr 660, Leu 661 and Glu 664. Atleast half a dozen hydrogen bonds are formed and an equally strong network of hydrophobic interactions has been observed. This appears to be an important site for carbohydrate recognition in the C-lobe of lactoferrin. Although its significance has not been fully understood it clearly appears to be a specific sugar binding site.