This is the N-terminal domain of ARMET proteins (also known as mesencephalic astrocyte-derived neurotrophic factor (MANF) or arginine-rich protein) [1,2,3], a saposin-like domain consisting of five alpha-helices with three cystein bridges that stabilises the globular "closed leaf" conformation [2,3]. ARMET is a small protein of approximately 170 residues which contain four di-sulfide bridges that are highly conserved from nematodes to humans. It is a soluble protein resident in the endoplasmic reticulum and induced by ER stress. It appears to be involved with dealing with mis-folded proteins in the ER, thus in quality control of ER stress [1].

1: ARMET is a Soluble ER Protein Induced by the Unfolded Protein Response via ERSE-II Element. Mizobuchi N, Hoseki J, Kubota H, Toyokuni S, Nozaki JI, Naitoh M, Koizumi A, Nagata K; Cell Struct Funct. 2007; [Epub ahead of print] PMID:17507765

2: Solution structure and dynamics of mouse ARMET. Hoseki J, Sasakawa H, Yamaguchi Y, Maeda M, Kubota H, Kato K, Nagata K; FEBS Lett. 2010;584:1536-1542. PMID:20214902

3: Unconventional neurotrophic factors CDNF and MANF: Structure, physiological functions and therapeutic potential. Lindahl M, Saarma M, Lindholm P; Neurobiol Dis. 2017;97:90-102. PMID:27425895