Human polyhomeotic homolog 3 (PHC3) sterile alpha motif (SAM) linker allows open-ended polymerization of PHC3 SAM.
Sterile alpha motifs (SAMs) are frequently found in eukaryotic genomes. An intriguing property of many SAMs is their ability to self-associate, forming an open-ended polymer structure whose formation has been shown to be essential for the function of the protein. What remains largely unresolved is how polymerization is controlled. Previously, we had determined that the stretch of unstructured residues N-terminal to the SAM of a Drosophila protein called polyhomeotic (Ph), a member of the polycomb group (PcG) of gene silencers, plays a key role in controlling Ph SAM polymerization. Ph SAM with its native linker created shorter polymers compared to Ph SAM attached to either a random linker or no linker. Here, we show that the SAM linker for the human Ph ortholog, polyhomeotic homolog 3 (PHC3), also controls PHC3 SAM polymerization but does so in the opposite fashion. PHC3 SAM with its native linker allows longer polymers to form compared to when attached to a random linker. Attaching the PHC3 SAM linker to Ph SAM also resulted in extending Ph SAM polymerization. Moreover, in the context of full-length Ph protein, replacing the SAM linker with PHC3 SAM linker, intended to create longer polymers, resulted in greater repressive ability for the chimera compared to wild-type Ph. These findings show that polymeric SAM linkers evolved to modulate a wide dynamic range of SAM polymerization abilities and suggest that rationally manipulating the function of SAM containing proteins through controlling their SAM polymerization may be possible.
Department of Biochemistry and CTRC, University of Texas Health Science Center at San Antonio, 78229-3990, United States.
Angela K
AK
Robinson
Belinda Z
BZ
Leal
David R
DR
Nanyes
Yogeet
Y
Kaur
Udayar
U
Ilangovan
Virgil
V
Schirf
Andrew P
AP
Hinck
Borries
B
Demeler
Chongwoo A
CA
Kim
D000595:Amino Acid Sequence; D000818:Animals; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D063150:Polycomb Repressive Complex 1 / Q000737:chemistry* / Q000378:metabolism; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D058767:Protein Unfolding; D017386:Sequence Homology, Amino Acid
C519295:PHC3 protein, human; D063150:Polycomb Repressive Complex 1