Calpain‐induced proteolysis of β‐spectrins

The calcium‐activated neutral protease calpain is activated in several pathological conditions. Calpain usually hydrolyses one or only a few peptide bonds in its substrate. One prominent substrate for calpain is spectrin and it has been shown that α‐spectrin is the preferred substrate. We now show that the β‐chain of spectrin is also a substrate for calpain proteolysis, and that the cleavage site in each β‐subunit is located at the very C‐terminal part of the molecule. Surprisingly, βIΣ1‐spectrin is cleaved at a different site than βIΣ2‐ and βIIΣ1‐spectrins despite their high degree of sequence identity.