Disease relevance of SMT1

• Escherichia coli extracts, obtained from a strain expressing the Arabidopsis SMT1 protein, can perform both the methyl and ethyl additions to appropriate sterol substrates, although with different kinetics [1].

High impact information on SMT1

• The availability of the SMT1 gene and mutant should permit the manipulation of phytosterol composition, which will help elucidate the role of sterols in animal nutrition [1].
• Sterol methyltransferase 1 controls the level of cholesterol in plants [1].
• The smt1 plants have pleiotropic defects: poor growth and fertility, sensitivity of the root to calcium, and a loss of proper embryo morphogenesis. smt1 has an altered sterol content: it accumulates cholesterol and has less C-24 alkylated sterols content [1].
• The Arabidopsis mutants fackel and sterol methyltransferase 1 have defects associated with body organization of the seedling [2].
• Thus it seems that C27-BRs, in addition to C28-BRs, are important in the production of more active C28-BRs and CS, where a SAM-dependent sterol methyltransferase appears to biosynthetically connect C27-BRs to C28-BRs [3].

Biological context of SMT1

• The fact that smt1 null mutants still produce alkylated sterols and that SMT1 can catalyze both alkylation steps shows that there is considerable overlap in the substrate specificity of enzymes in sterol biosynthesis [1].
• In both cases, several 24-ethyl- and 24-ethylidene sterols were synthetized indicating that the 4118 cDNA encodes a plant sterol C-methyltransferase able to perform two sequential methylations of the sterol side chain [4].

Anatomical context of SMT1

• Microsomes from erg6-4118-pYeDP60 were shown to possess AdoMet-dependent sterol-C-methyltransferase activity [5].

Associations of SMT1 with chemical compounds

• In SMT1 transformants a corresponding increase of alkylated sterols, mainly 24-methyl cholesterol, was observed [6].
• The ratio of campesterol to sitosterol that modulates growth in Arabidopsis is controlled by STEROL METHYLTRANSFERASE 2;1 [7].
• Delipidated preparations of these microsomes converted cycloartenol into 24-methylene cycloartanol and 24-methylene lophenol into 24-ethylidene lophenol, thus allowing the first identification of a plant sterol-C-methyltransferase cDNA [5].

Enzymatic interactions of SMT1

• The results suggest plant SMT2 has a position-specific substrate specificity for Delta(24(25))-sterols and contains a single active center to catalyze the consecutive C(1)-transfer activities by substrate reaction channels similar to the fungal SMT1 [8].

References