Interconversion of serine and glycine. (6R)-5,10-methylene-5,6,7,8-tetrahydrofolate + glycine + H2O = (6S)-5,6,7,8-tetrahydrofolate + L-serine One-carbon metabolism; tetrahydrofolate interconversion. Homotetramer (PubMed:7607226). Identified in complex with ABRAXAS2 and the other subunits of the BRISC complex, at least composed of ABRAXAS2, BRCC3/BRCC36, BABAM2 and BABAM1/NBA1. In eukaryotes there are two forms of the enzymes: a cytosolic one and a mitochondrial one. Belongs to the SHMT family.