α-Lactalbumin possesses a novel calcium binding loop

Abstract

Calcium performs a unique role in biology, achieving biological effects through highly specific interactions with and modulation of target proteins¹. It has been proposed that calcium-modulated proteins possess a characteristic, evolutionarily related, binding fold, known as the EF-hand². The high-resolution X-ray structure of α-lactalbumin reveals a Ca²⁺ binding fold that resembles an EF-hand only superficially and presumably has no evolutionary relationship with it. However, there is clear homology with the corresponding loop in c-type lysozyme (the ‘parent’ molecule of α-lactalbumin). This study, at 1.7 Å resolution, represents one of the most accurate analyses of a calcium binding protein yet reported.