Internally Deleted Human tRNA Synthetase Suggests Evolutionary Pressure for Repurposing

Abstract

SUMMARY Aminoacyl-tRNA synthetases (AARSs) catalyze aminoacylation of tRNAs in the cytoplasm. Surprisingly, AARSs also have critical extracellular and nuclear functions. Evolutionary pressure for new functions might be manifested by splice variants that skip only an internal catalytic domain (CD) and link non-catalytic N- and C-terminal polypeptides. Using disease-associated histidyl-tRNA synthetase (HisRS) as an example, we discovered an expressed 171 amino acid protein (HisRSΔCD) that deleted the entire CD, and joined an N-terminal WHEP to the C-terminal anticodon-binding domain (ABD). X-ray crystallographic and 3-D NMR methods revealed the first structures of human HisRS and HisRSΔCD. In contrast to homodimeric HisRS, HisRSΔCD is monomeric, where rupture of the ABD’s packing with CD resulted in a dumbbell-like structure of flexibly linked WHEP and ABD domains. In addition, the ABD of HisRSΔCD presents a new local conformation. This natural internally deleted HisRS suggests evolutionary pressure to reshape AARS tertiary and quaternary structures for repurposing.

Secreted Histidyl-tRNA Synthetase Splice Variants Elaborate Major Epitopes for Autoantibodies in Inflammatory Myositis

“…Interestingly, the first 60 aa of HisRS are encoded by the first two exons of the mRNA of HARS and are absent from HisRSs of prokaryotes and lower eukaryotes. As expected, anti-Jo-1 Abs do not react with Escherichia coli HisRS (9). According to our structural analysis, this small domain (designated as a WHEP domain) forms a helical coiled-coil structure (9).…”

“…As expected, anti-Jo-1 Abs do not react with Escherichia coli HisRS (9). According to our structural analysis, this small domain (designated as a WHEP domain) forms a helical coiled-coil structure (9). Other work showed that HisRS(1-48) induced migration of CD4 ϩ and CD8 ϩ lymphocytes, IL-2-activated monocytes, and immature dendritic cells.…”

“…In this in mind, we previously identified HisRS⌬CD, a natural HisRS SV that has an internal deletion that ablates the entire catalytic domain (CD) and joins the N-terminal WHEP domain (1-60 residues) to the C-terminal anticodon-binding domain (ABD) (9). The result is a change in both quaternary and tertiary structures.…”

“…Thus, HisRS⌬CD is a monomer (HisRS is a homodimer) shaped like a dumbbell-like structure, where a flexible linker joins its two domains and the ABD has an altered conformation. Although the epitopes were not mapped, HisRS⌬CD reacted with antiJo-1 Abs from patient sera (9).…”

“…Quantitative PCR and Data Analysis-Quantitative PCRs (qPCRs) were performed as described previously (9,11). The qPCR primer sequences were as follows: qFP1, CACGGTGCA-GAAGTCATTGAT; qRP1, TCCCCATACTTTCCCATCA-GTG; qFP2, GTGCTCAAAACCCCCAAGTAGAG; qRP2, C-ACAGTGGCTCACGCCTGT; qFP3, ACCCCCAAGTAG-AGACGAG; qRP3, TCTCGCGAACTGCCATCTG; qFP MXA , ACCTGATGGCCTATCACCAG; and qRP MXA , TTCAGGA-GCCAGCTGTAGGT.…”