1.A.113.5.1
Endoregulin, ELN, also called small integral membrane protein-6, SMIM6, is of 62 aas and 1 TMS.  This protein and the other members of the phospholamban family have been designated "micropeptides". Micropeptides function as regulators of calcium-dependent signaling in muscle. The sarco/endoplasmic reticulum Ca²⁺ ATPase (SERCA TC# 3.A.3.2.7), is the membrane pump that promotes muscle relaxation by taking up Ca²⁺ into the sarcoplasmic reticulum. It is directly inhibited by three known muscle-specific micropeptides: myoregulin (MLN), phospholamban (PLN) and sarcolipin (SLN). In non muscle cells, there are two other such micopeptides, endoregulin (ELN) and "another-regulin (ALN) (Anderson et al. 2016).  Endoregulin is also known as "small integral membrane protein-6" (SMIM6) while ALN is also known as Protein C4 orf3 (C4orf3).  These proteins share key amino acids with their muscle-specific counterparts and function as direct inhibitors of SERCA pump activity. The distribution of transcripts encoding ELN and ALN mirrored that of SERCA isoform-encoding transcripts in nonmuscle cell types. Thus, these two proteins are additional members of the SERCA-inhibitory micropeptide family, revealing a conserved mechanism for the control of intracellular Ca²⁺ dynamics in both muscle and nonmuscle cell types (Anderson et al. 2016).