Involved in the catabolism of vanillate and syringate. Catalyzes the transfer of a methyl moiety from vanillate or 3-O-methylgallate (3MGA) to tetrahydrofolate, forming protocatechuate (PCA) or gallate, respectively, and methyl-tetrahydrofolate. Has similar activities with both substrates (PubMed:15743951). Cannot use syringate (PubMed:15743951). Uses an ordered, sequential kinetic mechanism (PubMed:28373573). (6S)-5,6,7,8-tetrahydrofolate + vanillate = (6S)-5-methyl-5,6,7,8-tetrahydrofolate + 3,4-dihydroxybenzoate (6S)-5,6,7,8-tetrahydrofolate + 3-O-methylgallate = (6S)-5-methyl-5,6,7,8-tetrahydrofolate + 3,4,5-trihydroxybenzoate kcat is 5.76 sec(-1) with vanillate as substrate. Optimum pH is 8 with vanillate as substrate. Optimum temperature is 30 degrees Celsius with vanillate as substrate. Secondary metabolite metabolism; lignin degradation. Homodimer. Disruption of the gene leads to significant growth retardation on both vanillate and syringate. Belongs to the GcvT family.