About CALB / Calbindin:
With Calbindin, the clue is in the name. The CALcium-BINDINg proteins come in a group of three distinctive elements: Calbindin 1, Calbindin 2 or Calretinin, and Calbindin 3 or S100G. Initially discovered by researchers in fractions of chicken intestines and the intestines and kidneys of mammals, CALB proteins were first described as vitamin D-dependent calcium-binding proteins.
CALB proteins serve a unique role in helping to bind calcium in the micromolar range. Researchers have found a clear connection between vitamin D-deficiency and the reduced presence of CALB proteins.
CALB proteins exist in different sizes, with a molecular weight of approximately 9kDa and 28 kDa and 29 kDa. The subfamilies differ in their calcium-binding abilities and have different numbers of CA2+ binding structures or EF-hands.
Calbindin 1 is found in bird intestines and mammal kidneys. It also appears in a number of cells, both neuronal and endocrine. It is a 28 kDa protein in humans, which is encoded by the gene CALB1. The protein has 6 EF-hands, 4 of which have active CA2+ binding abilities. It mediates calcium absorption.
Calbindin 2 or Calretinin is primarily found in nervous tissues. It is a 29 kDa protein which counts 58% homology to Calbindin 1. It’s encoded by the gene CALB2. Structurally, the protein also consists of 6 EF-hands. CALB2 acts as a modulator of neuronal excitability. But it can also be used as a diagnostic marker for some human diseases and cancers.
Calbindin 3 or S100G is primarily found in mammalian intestines, but it can also appear in the kidneys and uterus. S100G is encoded by the gene CALB3 in humans. It is a lighter protein with only 2 EF-hands. CALB3 mediates calcium transport across intestine cells.