A helix-breaking mutation in TRPML3 leads to constitutive activity underlying deafness in the varitint-waddler mouse.
Homozygote varitint-waddler (Va) mice, expressing a mutant isoform (A419P) of TRPML3 (mucolipin 3), are profoundly deaf and display vestibular and pigmentation deficiencies, sterility, and perinatal lethality. Here we show that the varitint-waddler isoform of TRPML3 carrying an A419P mutation represents a constitutively active cation channel that can also be identified in native varitint-waddler hair cells as a distinct inwardly rectifying current. We hypothesize that the constitutive activation of TRPML3 occurs as a result of a helix-breaking proline substitution in transmembrane-spanning domain 5 (TM5). A proline substitution scan demonstrated that the inner third of TRPML3's TM5 is highly susceptible to proline-based kinks. Proline substitutions in TM5 of other TRP channels revealed that TRPML1, TRPML2, TRPV5, and TRPV6 display a similar susceptibility at comparable positions, whereas other TRP channels were not affected. We conclude that the molecular basis for deafness in the varitint-waddler mouse is the result of hair cell death caused by constitutive TRPML3 activity. To our knowledge, our study provides the first direct mechanistic link of a mutation in a TRP ion channel with mammalian hearing loss.
Departments of Otolaryngology, Head and Neck Surgery, and Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA.
Christian
C
Grimm
Math P
MP
Cuajungco
Alexander F J
AF
van Aken
Michael
M
Schnee
Simone
S
Jörs
Corné J
CJ
Kros
Anthony J
AJ
Ricci
Stefan
S
Heller
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D017209:Apoptosis; D002460:Cell Line; D034381:Hearing Loss / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D011392:Proline / Q000737:chemistry / Q000235:genetics; D017433:Protein Structure, Secondary / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D050053:TRPM Cation Channels / Q000235:genetics*; D050051:Transient Receptor Potential Channels
C470193:Mcoln3 protein, mouse; D050053:TRPM Cation Channels; D050051:Transient Receptor Potential Channels; D011392:Proline