Comparison of Holo-and Apo-Lactalbumin

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I. Introduction

Alpha-Lactalbumin regulates the lactose synthase complex.  This complex then catalyses the synthesis of lactose in the mammary glands when lactation occurs.  The native structure of α-Lactalbumin consists of two sub-domains, α-domain and the β-domain, that are divided by a cleft.  The α-domain has four α-helices and two short 310 helices.  The β-domain contains a triple-stranded anti-parallel β-sheet, a 310 helix and various loops.

For more information see Biochemistry Online: Chapter 2D - D:  PROTEIN FOLDING/STABILITY IN VIVO AND IN VITRO

II. General Structure

Lactalbumin with Calcium and TRP
Disulfide Bonds (4)
Backbone and sidechains
Cartoon, Hbonds and Wireframe
Comparison of Apo- and Holo- lactalbumin

The structural comparison of the apo vs. holo form of the protein was obtained at high ionic strength thus the structures appear more similar than they are.  High ionic strength was required to isolate the apo form of the protein, which is more unstable than the holo form, because the calcium ligand is absent.  Studies have shown that the high affinity of α-Lactalbumin for calcium is due to the fact that the electrostatic interactions of calcium with the binding site residues stabilizes the native form of the protein.  The actual differences is secondary structure of the apo- and holo- form of the protein are limited to the active site domain