We set out to determine whether the C-terminus (amino
acids 481–798)
of peroxisome proliferator-activated receptor gamma coactivator-1
alpha (PGC-1α, UniProt Q9UBK2), a regulatory metabolic protein
involved in mitochondrial biogenesis, and respiration, is an arginine
methyltransferase substrate. Arginine methylation by protein arginine
methyltransferases (PRMTs) alters protein function and thus contributes
to various cellular processes. In addition to confirming methylation
of the C-terminus by PRMT1 as described in the literature, we have
identified methylation by another member of the PRMT family, PRMT7.
We performed in vitro methylation reactions using
recombinant mammalian PRMT7 and PRMT1 at 37, 30, 21, 18, and 4 °C.
Various fragments of PGC-1α corresponding to the C-terminus
were used as substrates, and the methylation reactions were analyzed
by fluorography and mass spectrometry to determine the extent of methylation
throughout the substrates, the location of the methylated PGC-1α
arginine residues, and finally, whether temperature affects the deposition
of methyl groups. We also employed two prediction programs, PRmePRed
and MePred-RF, to search for putative methyltransferase sites. Methylation
reactions show that arginine residues R548 and R753 in PGC-1α
are methylated at or below 30 °C by PRMT7, while methylation
by PRMT1 was detected at these same residues at 30 °C. Computational
approaches yielded additional putative methylarginine sites, indicating
that since PGC-1α is an intrinsically disordered protein, additional
methylated arginine residues have yet to be experimentally verified.
We conclude that temperature affects the extent of arginine methylation,
with more methylation by PRMT7 occurring below physiological temperature,
uncovering an additional control point for PGC-1α.