Binding of smoothelin-like 1 to tropomyosin and calmodulin is mutually exclusive and regulated by phosphorylation.
The smoothelin-like 1 protein (SMTNL1) can associate with tropomyosin (Tpm) and calmodulin (CaM), two proteins essential to the smooth muscle contractile process. SMTNL1 is phosphorylated at Ser301 by protein kinase A during calcium desensitization in smooth muscle, yet the effect of SMTNL1 phosphorylation on Tpm- and CaM-binding has yet to be investigated.



Using pull down studies with Tpm-Sepharose and CaM-Sepharose, we examined the interplay between Tpm binding, CaM binding, phosphorylation of SMTNL1 and calcium concentration. Phosphorylation greatly enhanced the ability of SMTNL1 to associate with Tpm in vitro; surface plasmon resonance yielded a 10-fold enhancement in KDvalue with phosphorylation. The effect on CaM binding is more complex and varies with the availability of calcium.



Combining both CaM and Tpm with SMTNL1 shows that the binding to both is mutually exclusive.
Department of Biochemistry & Molecular Biology, University of Calgary, Cumming School of Medicine, 3280 Hospital Drive NW, Calgary, AB, T2N 4Z6, Canada.
Annegret
A
Ulke-Lemée
Department of Biochemistry & Molecular Biology, University of Calgary, Cumming School of Medicine, 3280 Hospital Drive NW, Calgary, AB, T2N 4Z6, Canada.
David Hao
DH
Sun
Biochemistry Research Group, Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, AB, T2N 1 N4, Canada.
Hiroaki
H
Ishida
Biochemistry Research Group, Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, AB, T2N 1 N4, Canada.
Hans J
HJ
Vogel
Department of Biochemistry & Molecular Biology, University of Calgary, Cumming School of Medicine, 3280 Hospital Drive NW, Calgary, AB, T2N 4Z6, Canada. jmacdo@ucalgary.ca.
Justin A
JA
MacDonald
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism*; D002645:Chickens; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D009124:Muscle Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009130:Muscle, Smooth / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000302:isolation & purification; D014335:Tropomyosin / Q000378:metabolism*
D002147:Calmodulin; D009124:Muscle Proteins; D011994:Recombinant Proteins; D014335:Tropomyosin; D017868:Cyclic AMP-Dependent Protein Kinases; D002118:Calcium
CHASM; Protein binding; SMTNL1; Smooth muscle; Thin filament