Identification of a novel calreticulin isoform (Crt2) in human and mouse
Introduction
Calreticulin (Crt) is a multi-functional protein localized mainly in the endoplasmic/sarcoplasmic reticulum (ER/SR) in most cells of all higher organisms (for review see; Michalak et al., 1992, Krause and Michalak, 1997, Michalak et al., 1999, Corbett and Michalak, 2000, Johnson et al., 2001). Although Crt has been suggested to be involved in over 40 intra- and extracellular processes, the research on Crt has mainly focused on its role in protein folding (Denecke et al., 1995, Hebert et al., 1996, Saito et al., 1999, Nakamura et al., 2001), and Ca2+-signaling (Camacho and Lechleiter, 1995, Mery et al., 1996, John et al., 1998, Nakamura et al., 2001, Persson et al., 2001).
Crt is an evolutionary highly conserved protein typically containing an HDEL/KDEL C-terminal ER-retention signal, and three major internal domains (Michalak et al., 1992, Michalak et al., 1999). These consist of a globular N-domain and two Ca2+-binding domains; a high-affinity but low-capacity P-domain, and a low-affinity but high-capacity C-domain. The P-domain has furthermore been shown to contain two triplets of conserved amino acid sequences necessary for the lectin-like chaperone function and potentially involved in the high-affinity Ca2+-binding properties of the protein (Baksh and Michalak, 1991). In addition, Crt typically contains an N-terminal signal sequence for ER-targeting, and three conserved cysteine residues involved in forming disulfide bridges to maintain proper folding of the protein (Matsuoka et al., 1994, Højrup et al., 2001).
Two or more genes encoding Crt isoforms have been found in Arabidopsis thaliana, Zea mays, Hordeum vulgare, Xenopus laevis and Bos taurus, but only one gene encoding Crt has previously been identified in human and mouse (McCauliffe et al., 1990, McCauliffe et al., 1992, Rooke et al., 1997). Furthermore, only one messenger RNA (mRNA) product had been identified in human and mouse, suggesting that there is no alternative splicing. The previously identified crt gene in human is located on chromosome 19 (19p13.2) (McCauliffe et al., 1990), and in mouse on chromosome 8 (Rooke et al., 1997). These two crt genes consist of nine exons with similar intron-exon organizations, and span a relatively short amount of genomic DNA (4.2 and 4.8 kb for human and mouse, respectively) (McCauliffe et al., 1992, Waser et al., 1997).
Here we report a novel crt isoform (crt2) expressed in testis in human, with an orthologue in mouse. The genomic structure, and chromosomal localization of the human crt2 is discussed, and the phylogenetic relationship of Crt proteins is described. Two additional crt2 isoforms, based on expressed sequence tag (EST) analysis, were discovered in pig and rat.
Section snippets
Sequence comparison of Crt proteins
Protein sequences corresponding to Homo sapiens Crt (denoted Crt1), Mus musculus Crt (denoted Crt1), B. taurus Crt1, Drosophila melanogaster Crt, A. thaliana Crt3, H. sapiens Crt2, and M. musculus Crt2 (GenBank Accession numbers AAA51916, CAA33053, AAB30209, CAA45791, AAC49697, XP_058951, and BAB24660, respectively), obtained from the GenBank database via NCBI (National Center for Biotechnology Information) (www.ncbi.nlm.nih.gov), were used for sequence analysis. ClustalW multiple alignments of
Identification of novel Crt isoforms
Performing standard BLASTP analysis at NCBI against Crt protein sequences from various species, we identified two novel Crt isoforms in human and mouse (GenBank Accession numbers: XP_058951 and BAB24660, respectively). The novel isoforms were for human 384 amino acids, and for mouse 380 amino acids in length. The sequences showed 53 and 49% identity, and 69 and 66% similarity to the previously identified Crt's in human and mouse, respectively [GenBank Accession numbers: AAA51916 (human) and
Acknowledgements
We thank Dr Urban Johanson and Magnus Alsterfjord for valuable discussions and advice regarding various analyzes. We also thank The Swedish Research Council for financial support.
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Phylogenetic analysis of plant calreticulin homologs
2019, Molecular Phylogenetics and EvolutionCitation Excerpt :The multifunctionality of CRT could be due to the existence of multiple genes. Two CRT genes, CRT1 and CRT2, have been identified in animals (Persson et al., 2002). In contrast, the plant CRT gene family comprises at least three members in two subclasses: CRT1/CRT2 (also known as CRT1a/CRT1b) and CRT3 (Persson et al., 2003; Jia et al., 2008).
Glycan specificity of a testis-specific lectin chaperone calmegin and effects of hydrophobic interactions
2014, Biochimica et Biophysica Acta - General SubjectsCitation Excerpt :X-ray diffraction study has revealed that the structure of the N-domain is globular and composed of β sandwich folds, while the P-domain holds a β strand hairpin form due to the presence of a proline-rich amino acid sequence [6]. Testis-specific chaperones calmegin (CMG) and calsperin (CRT3) are homologues of CNX and CRT, respectively [7–9]. Although CNX gene deletion was shown to cause early-postnatal death in mouse [10], CMG knockout mice were fully viable, while the generation of normal spermatozoa was affected [11].