- Ribonuclease T1
Ribonuclease T1 (sometimes abbreviated RNase T1) is a fungal
endonuclease that cleaves single-strandedRNA afterguanine residues, i.e., on their 3' end; the most commonly studied form of thisenzyme is the version found in themold "Aspergillus oryzae ". Owing to its specificity for guanine, RNase T1 is often used to digest denaturedRNA prior to sequencing. Similar to other ribonucleases such asbarnase and RNase A, ribonuclease T1 has been popular for folding studies. [cite journal | last = Pace | first = CN | coauthors = Heinemann U, Hahn U, Saenger W | year = 1991 | title = Ribonuclease T1: Structure, Function, and Stability | journal = Angewandte Cheni, International Edition | volume = 30 | pages = 343–360 | doi = 10.1002/anie.199103433]Structurally, ribonuclease T1 is a small α+β protein (104
amino acid s) with a four-stranded, antiparallelbeta sheet covering a longalpha helix (almost five turns). RNase T1 has two disulfide bonds, Cys2-Cys10 and Cys6-Cys103, of which the latter contributes more to its folding stability; [cite journal | last = Pace | first = CN | coauthors = Grimsley GR, Thomson JA, Barnett BJ | year = 1988 | title = Conformational stability and activity of ribonuclease T1 with zero, one, and two intact disulfide bonds | journal =Journal of Biological Chemistry | volume = 263 | pages = 11820–11825] complete reduction of both disulfides usually unfolds the protein, although its folding can be rescued with high salt concentrations. [cite journal | last = Oobatake | first = M | coauthors = Takahashi S, Ooi T | year = 1979 | title = Conformational stability of ribonuclease T1. II. Salt-induced renaturation | journal = Journal of Biochemistry (Tokyo) | volume = 86 | pages = 65–70]RNase T1 also has four
proline s, two of which (Pro39 and Pro55) have "cis"isomer s of their X-Propeptide bond s. Nonnative isomers of these prolines can retard conformational folding dramatically, [cite journal | last = Mayr | first = LM | coauthors = Odefey CO, Schutkowski M, Schmid FX | year = 1996 | title = Kinetic analysis of the unfolding and refolding of ribonuclease T1 by a stopped-flow double-mixing technique | journal = Biochemistry | volume = 35 | pages = 5550–5561 | doi = 10.1021/bi953035y] folding on a characteristic time scale of 7,000 seconds (almost two hours) at 10°C and pH 5. [cite journal | last = Mullins | first = LS | coauthors = Pace CN and Raushel FM | year = 1997 | title = Conformational stability of ribonuclease T1 measured by hydrogen-deuterium exchange | journal = Protein Science | volume = 6 | pages = 1387–1395]References
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