HSP40: Alternate Names
Figure 1. (click image for larger version)
Members of the 40 kDa heat shock protein family (DNAJ/HSP40) are characterized by the presence of the remarkably conserved J-domain, responsible for the regulation of the ATPase activity of HSP70s (Figure 1+2). Consequently, HSP40s are also designated as J-domain proteins (JDPs). The J-domain which was named after the founding member, the E. coli protein DnaJ, is about 70 amino acids in length and contains a conserved HPD tripeptide as the signature motif 32. Consequently, HSP40 family members are also termed DnaJ proteins (DNAJs). Historically, HSP40s/DNAJs have been classified into three subtypes/subfamilies (1, 2 and 3; also referred as to A, B, and C; Figure 1 33,34,35). Type 1 DNAJs/HSP40s are descendants of E. coli DnaJ and show a domain structure similar to that of DnaJ with the J-domain, the Gly/Phe(G/F)-rich region, the zinc finger (ZF) domain and a C-terminal extension. Type 2 DNAJ/HSP40 proteins bear the J-domain and the G/F-rich region, but lack the ZF domain. Figure 2. (click image for larger version)
Type 3 DNAJs/HSP40s do not have any of these conserved regions other than the J-domain. HSP40/DNAJ proteins bearing partially conserved J-like domains are designated as J- or DnaJ-like proteins. Members of the DNAJ/HSP40 family found in the ER are alternatively referred to as ER-localized DNAJ/HSP40 (Erdj) proteins. Six DnaJ/Hsp40 homologs have been found in E. coli including the eponymous type 1 family member DnaJ 6. Lower eukaryotes such as Saccharomyces cerevisiae express up to 22 DnaJ/Hsp40 homologs and several J-like proteins designated with different terms. Since the progressive expansion of the heat shock (stress) protein field has led to inconsistencies and a lack of clarity in the nomenclature for these families of molecules, Kampinga and colleagues have consequently proposed new guidelines to encourage the use of consistent and clear terminology 63. In accordance with this, human HSP40s are termed DNAJAs, DNAJBs, and DNAJCs in which the ending relates to the corresponding subfamily. Amongst them, DnaJB1 (UniProt ID#P25685; also known as Hdj1, Sis1, HSPF1) is the most widely expressed and heat-inducible isoform of human DnaJ/Hsp40. Table 2 lists various pro- and eukaryotic DNAJs/HSP40s together with their alternate names.