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Insights into the Regulatory Domain of Cystathionine Beta‐Synthase: Characterization of Six Variant Proteins
Author(s) -
Mendes Marisa I. S.,
Santos Ana Sofia,
Smith Desirée E. C.,
Lino Paulo Roque,
Colaço Henrique G.,
Almeida Isabel Tavares,
Vicente João B.,
Salomons Gajja S.,
Rivera Isabel,
Blom Henk J.,
Leandro Paula
Publication year - 2014
Publication title -
human mutation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 162
eISSN - 1098-1004
pISSN - 1059-7794
DOI - 10.1002/humu.22616
Subject(s) - cystathionine beta synthase , biology , serine , biochemistry , enzyme , allosteric regulation , mutant , gene , cysteine
ABSTRACT Cystathionine beta‐synthase ( CBS ) catalyzes the formation of cystathionine from homocysteine and serine. CBS is allosterically activated by S ‐adenosylmethionine ( SAM ), which binds to its C ‐terminal regulatory domain. Mutations in this domain lead to variants with high residual activity but lacking SAM activation. We characterized six C ‐terminal CBS variants (p. P 427 L , p. D 444 N , p. V 449 G , p. S 500 L , p. K 523 S fs*18, and p. L 540 Q ). To understand the effect of C ‐terminal mutations on the functional/structural properties of CBS , we performed dynamic light scattering, differential scanning fluorimetry, limited proteolysis, enzymatic characterization, and determination of SAM ‐binding affinity. Kinetic data confirm that the enzymatic function of these variants is not impaired. Although lacking SAM activation, the p. P 427 L and p. S 500 L were able to bind SAM at a lower extent than the wild type ( WT ), confirming that SAM binding and activation can be two independent events. At the structural level, the C ‐terminal variants presented various effects, either showing catalytic core instability and increased susceptibility toward aggregation or presenting with similar or higher stability than the WT . Our study highlights as the common feature to the C ‐terminal variants an impaired binding of SAM and no increase in enzymatic activity with physiological concentrations of the activator, suggesting the loss of regulation by SAM as a potential pathogenic mechanism.