Disulphide bonding in a stylar self-incompatibility ribonuclease of Nicotiana alata.
Many flowering plants have developed a self-incompatibility mechanism, which is controlled by a single polyallelic locus (the S-locus), to prevent inbreeding. The products of the S-locus in the styles of solanaceous plants are an allelic series of glycoproteins with RNase activity [McClure, B. A., Haring, V., Ebert, P. R., Anderson, M. A., Simpson, R. J., Sakiyama, F. & Clarke, A. E. (1989) Nature 342, 955-957]. These S-RNases show some amino-acid-sequence similarity with two fungal RNases (T2 and Rh), including the presence of two active-site His residues, which suggests a common three-dimensional structure. Disulphide bonding is important in the maintenance of the three-dimensional structure of the fungal RNases [Kurihara, H., Mitsui, Y., Ohgi, K., Irie, M., Mizuno, H. & Nakamura, T. (1992) FEBS Lett. 306, 189-192] and the S-RNases [Tsai, D. S., Lee, H.-S., Post, L. C., Kreiling, K. M. & Kao, T.-H. (1992) Sex. Plant Reprod. 5, 256-263]. We have used the S2-allele RNase of Nicotiana alata, which has nine Cys residues, to establish the pattern of disulphide bonding. The disulphide bonds Cys16-Cys21, Cys45-Cys94, Cys153-Cys182 and Cys165-Cys176 are consistent with the S2-RNase having a similar three-dimensional structure to RNase Rh. A free Cys residue (Cys95) adjacent to Cys45-Cys94 promotes a rapid specific disulphide migration when the protein is exposed to denaturing conditions.
Oxley
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Plant Cell Biology Research Centre, School of Botany, University of Melbourne, Parkville, Victoria, Australia.
Bacic
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D000595:Amino Acid Sequence; D002851:Chromatography, High Pressure Liquid; D004220:Disulfides / Q000378:metabolism*; D004722:Endoribonucleases / Q000737:chemistry / Q000378:metabolism; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D010947:Plants, Toxic; D012260:Ribonucleases / Q000737:chemistry* / Q000378:metabolism; D016415:Sequence Alignment; D014026:Nicotiana; D014357:Trypsin / Q000378:metabolism
D004220:Disulfides; D004722:Endoribonucleases; D012260:Ribonucleases; C075842:ribonuclease Rh; C022542:ribonuclease S; D014357:Trypsin