This is the Kringle-like domain (KLD) found in Melanocyte protein PMEL, Transmembrane glycoprotein NMB (GPNMB) and TMEM130, which is downstream the PKD domain. It contains six highly conserved cysteine residues that form the disulphide bonds of mature PMEL dimers. This domain is perfectly conserved in PMEL and GPNMB which suggests that GPNMB also forms dimers. PMEL and GPNMB, together with TMEM130 (its most ancient paralogue), have a conserved domain architecture and have been recently described as the PKAT (PKD- and KLD-Associated Transmembrane) protein family PMEL and GPNMB share overlapping phenotype and disease associations, such as melanin-based pigmentation, cancer, neurodegenerative disease and glaucoma.

1: Functional Domains and Evolutionary History of the PMEL and GPNMB Family Proteins. Chrystal PW, Footz T, Hodges ED, Jensen JA, Walter MA, Allison WT; Molecules. 2021; [Epub ahead of print] PMID:34207849