The functional properties of full length and mutant chicken gizzard smooth muscle caldesmon expressed in Escherichia coli

Wild type chicken gizzard caldesmon (756 amino acids) was expressed in a T7 RNA polymerase-based bacterial expression system at a yield of 1 mg pure caldesmon per litre bacterial culture. A mutant composed of amino acids 1-578 was also constructed and expressed. The wild type and mutant caldesmon were purified and compared with native chicken gizzard caldesmon. Native and wild type expressed caldesmon were indistinguishable in assays for inhibition of actin-tropomyosin activation of myosin ATPase, reversal of inhibition by Ca2+-calmodulin and binding to actin, actin-tropomyosin, Ca2+-calmodulin, tropomyosin and myosin. The mutant missing the C-terminal 178 amino acids had no inhibitory effect and did not bind to actin or Ca2+-calmodulin. It bound to tropomyosin with a 5-fold reduced affinity and to myosin with a greater than 10-fold reduced affinity.