(A) The Ca2+ pumps, RyR and SERCA, play a critical role in muscle contractility by controlling Ca2+ cycling between the cytosol and SR. MLN, PLN and SLN inhibit SERCA pump activity in different striated muscle types of vertebrates.
(B) Illustration of the family of SERCA-inhibitory micropeptides. The discovery of MLN reveals that vertebrates encode three SERCA-inhibitory peptides that share conserved residues within their transmembrane alpha helices. Green shading denotes identical residues and blue denotes similar residues. MLN, myoregulin; PLN, phospholamban; SLN, sarcolipin; SCL, sarcolamban.