SERCA

SERCA stands for Sarco/Endoplasmic Reticulum Ca²⁺-ATPase. It is a P-ATPase of the calcium ATPase type.

Function

SERCA resides in the sarcoplasmic reticulum (SR) within muscle cells. It is a Ca²⁺ ATPase which transfers Ca²⁺ from the cytosol of the cell to the lumen of the SR at the expense of ATP hydrolysis during muscle relaxation.

There are 3 major domains on the cytoplasmic face of SERCA: the phosphorylation and nucleotide-binding domains form the catalytic site, whereas the actuator domain is involved in the transmission of major conformational changes.

Regulation

SERCA is normally somewhat inhibited by a protein, phospholamban, with which it is closely associated.Another protein, calsequestrin, binds calcium within the SR and helps to reduce the concentration of free calcium within the SR, which assists SERCA so that it does not have to pump against such a high concentration gradient. The SR has a much higher concentration of Ca²⁺ (10,000x) inside when compared to the intracellular Ca²⁺ concentration.

The rate at which SERCA moves Ca²⁺ across the SR membrane can be controlled by phospholamban (PLB/PLN) under β-adrenergic stimulation. When PLB is associated with SERCA, the rate of Ca²⁺ movement is reduced, upon dissociation of PLB Ca²⁺ movement increases.

Paralogs

There are 3 major paralogs, SERCA1-3, which are expressed at various levels in different cell types.
* - SERCA1
* - SERCA2
* - SERCA3

There are additional post-translational isoforms of both SERCA2 and 3 which serve to introduce the possibility of cell type specific Ca²⁺-reuptake responses as well as increasing the overall complexity of the Ca²⁺ signalling mechanism.

External links

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