Alternative titles; symbolsCALMODULIN-LIKE SKIN PROTEIN; CLSPHGNC Approved Gene Symbol: CALML5Cytogenetic location: 10p15.1 Genomic coordinates (GRCh38): 10:...
Alternative titles; symbols
HGNC Approved Gene Symbol: CALML5
Cytogenetic location: 10p15.1 Genomic coordinates (GRCh38): 10:5,498,696-5,499,569 (from NCBI)
▼ Cloning and Expression
The stratum corneum, the uppermost layer of the human epidermis, provides the vital barrier between the organism and its environment. It is generated by keratinocytes that migrate from the basal layer to the surface of the epidermis undergoing terminal differentiation, a process that is calcium dependent. Low concentrations of calcium in the basal layer of the epidermis favor keratinocyte proliferation, and an increasing calcium gradient toward the surface controls part of the complex differentiation. Thus, calcium-binding proteins, which mediate calcium signals by interacting with and modulating specific target proteins, are important for epidermal differentiation. Using 2-dimensional gel electrophoresis, Mehul et al. (2000) separated an extract of total proteins from human stratum corneum. Peptide sequence analysis of 2 spots, followed by a homology search, revealed identification of a novel calcium-binding protein of the calmodulin (e.g., CALM1; 114180) family that the authors named 'calmodulin-like skin protein' (CLSP). By PCR using a degenerate oligonucleotide based on a CLSP peptide sequence, and 2 human keratinocyte cDNA libraries, one derived from proliferating cultured keratinocytes and the other from differentiated keratinocytes of reconstructed epidermis, Mehul et al. (2000) isolated a full-length CLSP cDNA. The predicted 146-amino acid CLSP protein contains 4 putative EF-hands, which are domains that bind to calcium, 2 potential sites for N-glycosylation, multiple potential sites for phosphorylation, and 1 potential site for myristoylation. CLSP shares 52% amino acid sequence homology with human calmodulin. RT-PCR of various human tissues and reconstructed epidermis detected abundant CLSP expression only in epidermis, with very low expression in lung. Evaluation of CLSP expression during keratinocyte differentiation revealed that CLSP was not detectably expressed in proliferating keratinocytes but was expressed in differentiating keratinocytes, beginning at an advanced stage of differentiation.
Hwang and Morasso (2003) cloned mouse Scarf (skin calmodulin-related factor), the likely ortholog of human CLSP. The deduced 148-amino acid Scarf protein contains 4 EF-hand domains and shares 64.9% identity with human CLSP. Scarf has a slightly extended central helix compared with human CLSP. Northern and RNA dot blot analyses of adult mouse tissues detected Scarf only in thyroid and skeletal muscle. Northern blot analysis and RT-PCR showed strong Scarf expression in keratinocytes, with expression first detected at embryonic day 15. In situ hybridization localized Scarf within the spinous and granular layers in stratified epidermis, but not in the basal layer, of 16-day mouse embryos. In situ hybridization and immunohistochemical analysis of neonatal skin revealed Scarf only in anucleated differentiated layers of stratified epidermis. Hwang and Morasso (2003) noted that both Scarf and human CLSP are expressed predominantly in differentiated keratinocytes, but that Scarf is expressed earlier than CLSP during the differentiation process. In addition, Scarf and CLSP show slightly different distributions in other tissues.
▼ Gene Function
Mehul et al. (2000) demonstrated that recombinant CLSP could bind calcium, and like calmodulin, thereafter exposed hydrophobic regions, which most likely interact with target proteins. Sequencing of an epidermal protein retained by a CLSP affinity column revealed 100% identity with transglutaminase-3 (TGM3; 600238), which is a key enzyme in terminal epidermal differentiation. Mehul et al. (2000) suggested that CLSP may play an important role in late keratinocyte differentiation.
Hwang and Morasso (2003) showed that mouse Scarf could bind Ca(2+) in an in vitro Ca(2+)-binding assay. Mutations in each of the EF-hand motifs diminished the ability of Scarf to bind Ca(2+).
Hartz (2010) mapped the CALML5 gene to chromosome 10p15.1, based on an alignment of the CALML5 sequence (GenBank AF172852) with the genomic sequence (GRCh37).
Hwang and Morasso (2003) found that the mouse Scarf gene is duplicated. The 2 copies, Scarf and Scarf2, map about 15 kb apart on chromosome 13. This region of mouse chromosome 13 appears syntenic with human chromosome 10, but humans do not have an ortholog of Scarf2.