L-histidyl-[protein] + S-adenosyl-L-methionine => N(pros)-methyl-L-histidyl-[protein] + S-adenosyl-L-homocysteine + H(+)
l-histidyl-[protein] + s-adenosyl-l-methionine => n(pros)-methyl-l-histidyl-[protein] + s-adenosyl-l-homocysteine + h(+)