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Dynamics of the tRNase Z Flexible Arm
Author(s) -
Wilson Christopher,
Levinger Louis,
Chang Emmanuel,
Lama Neema,
Sabry May,
Rai Rita,
Paul Sabina
Publication year - 2010
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.24.1_supplement.499.12
Subject(s) - stalk , stereochemistry , chemistry , transfer rna , amino acid , crystallography , rna , biology , biochemistry , gene , horticulture
Pre‐tRNAs are transcribed as precursors which undergo maturation including cleavage of 5′ and 3′ extensions and 3′ end CCA addition. The 3′ trailer is endonucleolytically removed by tRNase Z, a member of the β‐lactamase superfamily of metal‐dependent hydrolases. The body of the enzyme consists of a four‐layer alpha‐beta sandwich including the conserved metal‐coordinating HxHxDH motif. tRNAse Z features a unique protruding flexible arm (FA), an ααββ hand connected to the body of the enzyme by ascending and descending stalks, involved with recognition and binding of the elbow of pre‐tRNA. Deletion of the FA hand increases K M ~70‐fold relative to wild‐type tRNase Z. A 40‐residue Ala‐scan revealed two regions that are critical for binding (Figure), a leucine at the ascending stalk/α4 boundary at which Ala substitution increases K M ~40‐fold, and a glycine‐proline (GP) rich loop that connects α4/α5. Vertebrates have a conserved GP loop TAAIA insertion which could affect the FA‐substrate interaction based on homology modeling. The stalk is structured by an inter‐strand H‐bond network. Hand–stalk geometry is maintained in free enzyme by a conserved H‐bond between a lysine in the hand and a glycine in the stalk. The stalk and first α helix swing back from the body of the enzyme when tRNA is bound. Upon tRNA binding, the ε‐NH 2 group of the lysine flips toward substrate, breaking its bond with glycine in the stalk and forming a bond with a T‐loop phosphate. The lysine is susceptible to trypsin, suggesting that its exposure to solvent could be a useful reporter of FA structure. Supported by the NIH.