The cationic porphyrin TMPyP4 destabilizes the tetraplex form of the fragile X syndrome expanded sequence d(CGG)n.
Fragile X syndrome, the most common cause of inherited mental retardation, is instigated by dynamic expansion of a d(CGG) trinucleotide repeat in the 5'-untranslated region of the first exon of the FMR1 gene, resulting in its silencing. The expanded d(CGG)(n) tract readily folds into hairpin and tetraplex structures which may contribute to the blocking of FMR1 transcription. In this work, we report that the cationic porphyrin 5,10,15,20-tetra(N-methyl-4-pyridyl)porphin (TMPyP4) effectively destabilizes in vitro the G'2 bimolecular tetraplex structure of d(CGG)(n) while it stabilizes the G'2 tetraplex form of the telomeric sequence d(TTAGGG)(2). Similarly to TMPyP4, the hnRNP-related protein CBF-A also destabilizes G'2 tetrahelical d(CGG)(n) while binding and stabilizing tetraplex telomeric DNA. We report that relative to each agent individually, successive incubation of G'2 d(CGG)(n) with TMPyP4 followed by exposure to CBF-A results in a nearly additive extent of disruption of this tetraplex form of the repeat sequence. Our observations open up the prospect of unfolding secondary structures of the expanded FMR1 d(CGG)(n) tract of fragile X cells by their exposure to low molecular size drugs or to proteins such as TMPyP4 or CBF-A.
Weisman-Shomer
Pnina
P
Unit of Biochemistry, The Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, PO Box 9649, Haifa 31096, Israel.
Cohen
Esther
E
Hershco
Inbal
I
Khateb
Samer
S
Wolfovitz-Barchad
Orit
O
Hurley
Laurence H
LH
Fry
Michael
M
D001667:Binding, Competitive; D004247:DNA / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019175:DNA Methylation; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism; D051860:Fragile X Messenger Ribonucleoprotein 1; D007700:Kinetics; D009419:Nerve Tissue Proteins / Q000235:genetics*; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D009841:Oligonucleotides / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011166:Porphyrins / Q000737:chemistry* / Q000378:metabolism; D016601:RNA-Binding Proteins; D012097:Repressor Proteins / Q000737:chemistry / Q000378:metabolism; D013696:Temperature; D019680:Trinucleotide Repeat Expansion / Q000235:genetics*
D004247:DNA; D004268:DNA-Binding Proteins; D051860:Fragile X Messenger Ribonucleoprotein 1; D009419:Nerve Tissue Proteins; D009841:Oligonucleotides; D011166:Porphyrins; D016601:RNA-Binding Proteins; D012097:Repressor Proteins; C021096:tetra(4-N-methylpyridyl)porphine