Catalyzes the transfer of a methyl group from 5-methyltetrahydrofolate to homocysteine resulting in methionine formation. 5-methyltetrahydropteroyltri-L-glutamate + L-homocysteine = L-methionine + tetrahydropteroyltri-L-glutamate Binds 2 Zn(2+) ions per subunit. Amino-acid biosynthesis; L-methionine biosynthesis via de novo pathway; L-methionine from L-homocysteine (MetE route): step 1/1. Expressed in pollen (at protein level). Causes an allergic reaction in human. Binds to IgE in patients allergic to the pollen of prickly saltwort. Both the recombinant 45 kDa N-terminal fragment and the 39 kDa C-terminal fragment of this protein bind to IgE in 67% of the 12 prickly saltwort pollen-allergic patients tested. The same patients have also a positive skin prick test (SPT) response toward these fragments. Belongs to the vitamin-B12 independent methionine synthase family.