Catalyzes the reversible interconversion of alpha-methyl-L-serine to D-alanine with tetrahydrofolate (THF) serving as the one-carbon carrier. Cannot use alpha-methyl-D-serine, L-serine, D-serine or L-alanine. (6R)-5,10-methylene-5,6,7,8-tetrahydrofolate + D-alanine + H2O = (6S)-5,6,7,8-tetrahydrofolate + 2-methylserine Inhibited by hydroxylamine and sodium borohydride. Optimum pH is 7.4-8.0. One-carbon metabolism; tetrahydrofolate interconversion. Homodimer. Belongs to the SHMT family.