max)The endoplasmic reticulum (ER) immunoglobulin binding proteins (BiPs) are molecular chaperones involved in normal protein maturation and refolding malformed proteins through the unfolded protein response (UPR). Plants BiPs belong to a multi-gene family contributing to development, immunity, and responses to environmental stresses. This study identified three BiP homologues in the Solanum tuberosum (potato) genome using phylogenetic, amino acid sequence, 3-D protein modeling and gene structure analysis. These analyses revealed that StBiP1 and StBiP2 grouped with AtBiP2, whereas StBiP3 grouped with AtBiP3. While the protein sequences and folding structures are highly similar, these StBiPs are distinguishable by their expression patterns in different tissues and in response to environmental stressors such as treatment with heat, chemicals, or virus elicitors of UPR. Ab initio promoter analysis revealed that potato and Arabidopsis BiP1 and BiP2 promoters were highly enriched with cis regulatory elements (CREs) linked to developmental processes, whereas BiP3 promoters were enriched with stress-related CREs. The frequency and linear distribution of these CREs produced two phylogenetic branches that further resolve the groups identified through gene phylogeny and exon/intron phase analysis. These data reveal that the CRE architecture of BiP promoters potentially define their spatio -temporal expression patterns under developmental and stress related cues.
IntroductionThe ER binding immunoglobulin protein (BiP), also known as the glucose receptor protein 78 (GRP78) is conserved across evolutionary kingdoms and is one of the best characterized molecular chaperones in the endoplasmic reticulum (ER). BiP guides the cotranslational translocation of nascent proteins into the ER, chaperones protein folding and maturation. BiP plays a key role in protein quality control by identifying and refolding misfolded proteins. BiP directs the post-translational translocation of proteins out of the ER. BiP contains an N-terminal nucleotide-binding domain (NBD) and a C-terminal substrate-binding domain (SBD). The NBD consists of two lobes surrounding the allosteric ATP-binding site, which modulates the substrate-binding activities. SBD consists of two subdomains, SBDβ and SBDα, which enable BiP to bind the hydrophobic surfaces of newly translated proteins to protect them from aggregation in an ATP-dependent manner. The SBDβ is a pocket with two primary loops that surround the nascent polypeptide and, the SBDα lid is covering this pocket 1 . All BiP proteins have C-terminal HDEL or KDEL signaling motif, which ensures their retention and function in the ER and an ATP-binding domain near the N-terminus 2 .Across eukaryotes, BiPs are among the most abundant chaperones in the ER and are directly engaged in regulating the unfolded protein response (UPR). Under normal conditions in mammalian cells, BiP binds to and inhibits the three ER stress sensors, protein kinase RNA-like ER kinase (PERK), activating transcription factor 6 (ATF6), and in...