N-helix and Cysteines Inter-regulate Human Mitochondrial VDAC-2 Function and Biochemistry.
Human voltage-dependent anion channel-2 (hVDAC-2) functions primarily as the crucial anti-apoptotic protein in the outer mitochondrial membrane, and additionally as a gated bidirectional metabolite transporter. The N-terminal helix (NTH), involved in voltage sensing, bears an additional 11-residue extension (NTE) only in hVDAC-2. In this study, we assign a unique role for the NTE as influencing the chaperone-independent refolding kinetics and overall thermodynamic stability of hVDAC-2. Our electrophysiology data shows that the N-helix is crucial for channel activity, whereas NTE sensitizes this isoform to voltage gating. Additionally, hVDAC-2 possesses the highest cysteine content, possibly for regulating reactive oxygen species content. We identify interdependent contributions of the N-helix and cysteines to channel function, and the measured stability in micellar environments with differing physicochemical properties. The evolutionary demand for the NTE in the presence of cysteines clearly emerges from our biochemical and functional studies, providing insight into factors that functionally demarcate hVDAC-2 from the other VDACs.
From the Department of Biological Sciences, Molecular Biophysics Laboratory, Indian Institute of Science Education and Research, Bhopal 462023, India.
Svetlana Rajkumar
SR
Maurya
From the Department of Biological Sciences, Molecular Biophysics Laboratory, Indian Institute of Science Education and Research, Bhopal 462023, India maha@iiserb.ac.in.
Radhakrishnan
http://orcid.org/0000-0003-1549-7550
R
Mahalakshmi
D003545:Cysteine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006801:Humans; D015640:Ion Channel Gating; D024101:Mitochondrial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017433:Protein Structure, Secondary; D013329:Structure-Activity Relationship; D013816:Thermodynamics; D050996:Voltage-Dependent Anion Channel 2 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
D024101:Mitochondrial Proteins; C494765:VDAC2 protein, human; D050996:Voltage-Dependent Anion Channel 2; D003545:Cysteine
N-terminal domain; gating; ion channel; membrane protein; protein folding; thermodynamics; voltage-dependent anion channel (VDAC)