Purification and Characterisation of Survivin Homologs

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Purification and characterisation of survivin homologs

Sanjogta Koul

School of Biotechnology, University of Jammu

Guided by

Dr. Shekhar C. Mande

Lab of Structural Biology, National Centre for Cell Sciences, Pune 411007

1. Introduction

Human survivin is a 16.5 kDa i.e., 142 amino acid protein. It is a member of inhibitor of apoptosis

protein (IAP) family. It is mainly expressed during the G

M phase of the cell cycle and is hypothesized

to inhibit many apoptotic cascades. It is generally overexpressed in tumour cells.

1.1. Structure of survivin

The structure of human survivin consists of N-terminal Zn

- binding BIR (Baculovirus IAP Repeat)

domain which is linked to a 65 Å amphipathic C-terminal alpha-helix.

In the BIR domain, three stranded antiparallel β-sheets are present which are surrounded by four small

α-helices. In this BIR domain a Zn

ion is present which is tetrahedrally coordinated by Cys 57, Cys

60, His 77, and Cys 84 bridges the core β-sheet with α4 and α5 helices [1].

Survivin’s unique feature is the presence of a 65 Å long C-terminal helix, α6, residues 100–140. Both

hydrogen bonding and hydrophobic interactions stabilize and fixes the direction of helical cord

between the BIR domain and residues of α6.

Human survivin exists as a dimer when alone and forms a bow-tie shaped dimer between the two α6

helices and form an 110° angle approximately with a tip-to-tip interhelical distance of 111 Å. But when

it is alone [2].

Fig. 1. Overall architecture of human survivin. (a) Ribbon representation of the survivin dimer. The

Zn2+ ion is shown as a shaded sphere. Coordination bonds are shown as dotted orange spheres. One

monomer is blue; the other is rose. (b) Orthogonal view of the ribbon representation shown in (a). (c)

Perspective and close up view of the Zn2+ binding site on one survivin monomer. The depicted

orientation corresponds to that pictured in (a) [1].

1.2. Interaction of Survivin with other proteins

Survivin when exists as a monomer, interacts by hydrophobic interactionswith INCENP, Borealin and

aurora kinase B (AUKB) and forms chromosomal passenger complex (CPC) thus participating in cell

division.