Serine hydroxymethyltransferase (SHMT) is an enzyme (EC18.104.22.168) which plays an important role in cellular one-carbon pathways by catalyzing the reversible, simultaneous conversions of L-serine to glycine (retro-aldol cleavage) and tetrahydrofolate to 5,10-methylenetetrahydrofolate (hydrolysis). This reaction provides the largest part of the one-carbon units available to the cell.
As well as its primary role in folate metabolism, SHMT also catalyzes other reactions that may be biologically significant, including the conversion of 5,10-methenyltetrahydrofolate to 10-formyltetrahydrofolate. When coupled with C1-tetrahydrofolate synthase and tetrahydropteroate, cSHMT also catalyzes the conversion of formate to serine.
Smith-Magenis syndrome (SMS) is a rare disorder that manifests as a complex set of traits including facial abnormalities, unusual behaviors, and developmental delay. It results from an interstital deletion within chromosome 17p11.2, including the cSHMT gene and a small study showed SHMT activity in SMS patients was ~50% of normal. Reduced SHMT would result in less glycine which could affect the nervous system by acting as an agonist to the NMDA receptor and this could be a mechanism behind SMS.
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