Increased hydrophobicity at the N terminus/membrane interface impairs gating of the severe combined immunodeficiency-related ORAI1 mutant.
Patients with severe combined immune deficiency (SCID) suffer from defective T-cell Ca2+ signaling. A loss of Ca2+ entry has been linked at the molecular level to single missense mutation R91W in the store-operated Ca2+ channel ORAI1. However, the mechanistic impact of this mutation on ORAI1 function remains unclear. Confocal Förster resonance energy transfer microscopy revealed that dynamic store-operated coupling of STIM1 to ORAI1 R91W was largely sustained similar to wild-type ORAI1. Characterization of various point mutants at position 91 by whole cell patch clamp recordings displayed that neutral or even negatively charged amino acids did not abolish ORAI1 function. However, substitution by hydrophobic leucine, valine, or phenylalanine resulted in non-functional ORAI1 channels, despite preserved STIM1 coupling. Besides conformational constraints at the N terminus/membrane interface predicted for the hydrophobic mutants, additional key factor(s) were suggested to determine ORAI1 functionality. Calculation of the probability for the 1st transmembrane domain and its hydrophobicity revealed a substantial increase for all hydrophobic substitutions that lead to non-functional ORAI1 R91X mutants in contrast to those with hydrophilic residues. Hence, increased hydrophobicity might lead to disrupted permeation/gating, as an ORAI1 channel with increased pore size and R91W mutation failed to recover activity. In conclusion, the increase in hydrophobicity at the N terminus/membrane interface represents the major cause for yielding non-functional ORAI1 channels.
Institute for Biophysics, University of Linz, Altenbergerstrasse 69, 4040 Linz, Austria.
Isabella
I
Derler
Marc
M
Fahrner
Oliviero
O
Carugo
Martin
M
Muik
Judith
J
Bergsmann
Rainer
R
Schindl
Irene
I
Frischauf
Said
S
Eshaghi
Christoph
C
Romanin
D019943:Amino Acid Substitution; D015220:Calcium Channels / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D003001:Cloning, Molecular; D019295:Computational Biology; D031541:Fluorescence Resonance Energy Transfer; D005998:Glycine / Q000378:metabolism; D006801:Humans; D007668:Kidney / Q000196:embryology / Q000502:physiology; D007700:Kinetics; D016297:Mutagenesis, Site-Directed; D000071740:ORAI1 Protein; D015183:Restriction Mapping; D012694:Serine / Q000378:metabolism; D016511:Severe Combined Immunodeficiency / Q000235:genetics*; D014162:Transfection
D015220:Calcium Channels; D000071740:ORAI1 Protein; C510746:ORAI1 protein, human; D012694:Serine; D005998:Glycine