S-adenosyl-L-methionine-dependent transferase that acts as a component of the wybutosine biosynthesis pathway. Wybutosine is a hyper modified guanosine with a tricyclic base found at the 3'-position adjacent to the anticodon of eukaryotic phenylalanine tRNA. Catalyzes the transfer of the alpha-amino-alpha-carboxypropyl (acp) group from S-adenosyl-L-methionine to the C-7 position of 4-demethylwyosine (imG-14) to produce wybutosine-86 (By similarity). 4-demethylwyosine(37) in tRNA(Phe) + S-adenosyl-L-methionine = 4-demethyl-7-[(3S)-3-amino-3-carboxypropyl]wyosine(37) in tRNA(Phe) + H(+) + S-methyl-5'-thioadenosine tRNA modification; wybutosine-tRNA(Phe) biosynthesis. Belongs to the class I-like SAM-binding methyltransferase superfamily. TRM5/TYW2 family.