Open AccessThe microheterogeneity of the crystallizable yeast cytoplasmic aspartyl‐tRNA synthetase
Author(s) -
LORBER Bernard,
KERN Daniel,
MEJDOUB Hafedh,
BOULANGER Yves,
REINBOLT Joseph,
GIEGÉ Richard
Publication year - 1987
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1987.tb11454.x
Subject(s) - chromatofocusing , enzyme , yeast , biochemistry , proteolysis , transfer rna , polyacrylamide gel electrophoresis , chemistry , isoelectric focusing , isoelectric point , gel electrophoresis , cytoplasm , biology , rna , gene
Yeast aspartyl‐tRNA synthetase is a dimeric enzyme (α 2 , M r 125000) which can be crystallized either alone or complexed with tRNA Asp . When analyzed by electrophoretic methods, the pure enzyme presents structural heterogeneities even when recovered from crystals. Up to three enzyme populations could be identified by polyacrylamide gel electrophoresis and more than ten by isoelectric focusing. They have similar molecular masses and mainly differ in their charge. All are fully active. This microheterogeneity is also revealed by ion‐exchange chromatography and chromatofocusing. Several levels of heterogeneity have been defined. A first type, which is reversible, is linked to redox effects and/or to conformational states of the protein. A second one, revealed by immunological methods, is generated by partial and differential proteolysis occurring during enzyme purification from yeast cells harvested in growth phase. As demonstrated by end‐group analysis, the fragmentation concerns exclusively the N‐terminal end of the enzyme. The main cleavage points are Gln‐19, Val‐20 and Gly‐26. Six minor cuts are observed between positions 14 and 33. The present data are discussed in the perspective of the crystallographic studies on aspartyl‐tRNA synthetase.