Question

The second part of the mechanism for histidyl-tRNA-synthetase is shown below. Active site residues are in black and the substrates are shown in green. Examine the image and complete the following questions. RNAH A76 Arg113 Gin 127 Glu131 M-o Histidy-Adenylate Arg259 Tyr264 c 1. Describe the role of Arg259 in the active site of histidyl- RNA-synthetase. Proton anor acid 2. If the substrates for this enzyme are histidine, ATP, and tRNAHs. Describe overall (not mechanism steps) what must have happened prior to the part of the mechanism shown above. tPNA tvansports nistiayl-tN to ER, Wnini it hindr to 6in121 to 1xain suns 3. Describe, in detail, the first step in the mechanism shown above. GIn 121 0cts as an adia donatS a pair of electroruS 4. Describe the role of Giní27 in the second step of the mechanism euciopt Predict the product of this mechanism. 5. Bonus: What enzyme class would this enzyme belong to? LYS0SAT Yo

Answer 1

Dear Student,

Please find the below answers:-

1. Histidyl tRNA synthetase uses the Arg259 as the positive charged substitute for the Histidine activation.
2. Prior to the mechanism shown here, induced fit mechanism occurs by two important conformational changes. First part consist of the conformational change occurs at the Histidine-1 loop with the help of Arg259, in which Tyr-264 residues construct the histidine side-chain binding pocket. Catalytic Arg-259 forms hydrogen bonds to Tyr-264, Glu-131 and the histidine carboxyl group, allowing for the correct positioning of the complex structure. Second, histidine binding induces conformational change at the “ordering loop”, by which residues 57 to 62  undergo the disordered/ordered transition of the ordering loop. Two hydrogen bonds hold the closed structure of the histidine binding loop and ordering loop.
3. The positively charged Arg259 would donate the positive charge to activate the histidine.
4. The role of Gln127 in second step of this mechanism is to provide hydrogen bonding with the histidine.
5. The product of this mechanism is the addition of one another amino acid in peptide chain during protein synthesis.
6. This enzyme belongs to transferease class of enzymes.