Structure, binding interface and hydrophobic transitions of Ca2+-loaded calbindin-D28K

Abstract

Calbindin-D(28K) is a Ca2+-binding protein, performing roles as both a calcium buffer and calcium sensor. The NMR solution structure of Ca2+-loaded calbindin-D(28K) reveals a single, globular fold consisting of six distinct EF-hand subdomains, which coordinate Ca2+ in loops on EF1, EF3, EF4 and EF5. Target peptides from Ran-binding protein M and myo-inositol monophosphatase, along with a new target from procaspase-3, are shown to interact with the protein on a surface comprised of alpha5 (EF3), alpha8 (EF4) and the EF2-EF3 and EF4-EF5 loops. Fluorescence experiments reveal that calbindin-D(28K) adopts discrete hydrophobic states as it binds Ca2+. The structure, binding interface and hydrophobic characteristics of Ca2+-loaded calbindin-D(28K) provide the first detailed insights into how this essential protein may function. This structure is one of the largest high-resolution NMR structures and the largest monomeric EF-hand protein to be solved to date.

Binding of calcium ions and SNAP-25 to the hexa EF-hand protein secretagogin

“…Well-known members of the HEF group are calbindin D 28k and calretinin. A high-resolution structure was recently presented for calbindin D 28k [8], showing a single globular domain comprising all six EF-hands in agreement with earlier fragment complementation studies [9,10]. Secretagogin exists in three different forms, two of which are characterized by a single amino acid exchange [glutamine (Q)/arginine (R)] at residue 22 (secretagogin Q-22 and secretagogin R-22) [11].…”

Cytosolic Ca2+ Buffers

“…The four medium/high affinity sites (Nagerl et al 2000) are considered Ca 2þ -specific, albeit low affinity Mg 2þ binding (K D,Mg % 700 mM) to the same sites at physiological [Mg 2þ ] i decreases the apparent Ca 2þ affinity approximately two-fold; additionally, Mg 2þ binding increases the cooperativity of Ca 2þ binding (Berggard et al 2002a). The NMR solution structure of Ca 2þ -bound rat CB-D28k reveals that it consists of a single, almost globular (ellipsoid) fold with six distinguishable EFhand domains (Kojetin et al 2006) (Fig. 1).…”

Influence of oral administration of HMB to pregnant dams on calbindin expression in the dentate gyrus of the hippocampus during postnatal development in spiny mice offspring

“…Neuronal calcium levels are strictly regulated by calcium-binding proteins. These include the calbindin--D28k (CB), a buffering and sensory protein (13,21).…”