Caspase-6 Undergoes a Distinct Helix-Strand Interconversion upon Substrate Binding.
Caspases are cysteine aspartate proteases that are major players in key cellular processes, including apoptosis and inflammation. Specifically, caspase-6 has also been implicated in playing a unique and critical role in neurodegeneration; however, structural similarities between caspase-6 and other caspase active sites have hampered precise targeting of caspase-6. All caspases can exist in a canonical conformation, in which the substrate binds atop a β-strand platform in the 130's region. This caspase-6 region can also adopt a helical conformation that has not been seen in any other caspases. Understanding the dynamics and interconversion between the helical and strand conformations in caspase-6 is critical to fully assess its unique function and regulation. Here, hydrogen/deuterium exchange mass spectrometry indicated that caspase-6 is inherently and dramatically more conformationally dynamic than closely related caspase-7. In contrast to caspase-7, which rests constitutively in the strand conformation before and after substrate binding, the hydrogen/deuterium exchange data in the L2' and 130's regions suggested that before substrate binding, caspase-6 exists in a dynamic equilibrium between the helix and strand conformations. Caspase-6 transitions exclusively to the canonical strand conformation only upon substrate binding. Glu-135, which showed noticeably different calculated pKavalues in the helix and strand conformations, appears to play a key role in the interconversion between the helix and strand conformations. Because caspase-6 has roles in several neurodegenerative diseases, exploiting the unique structural features and conformational changes identified here may provide new avenues for regulating specific caspase-6 functions for therapeutic purposes.
From the Departments of Chemistry and.
Kevin B
KB
Dagbay
From the Departments of Chemistry and.
Nicolas
N
Bolik-Coulon
Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Massachusetts 01003.
Sergey N
SN
Savinov
From the Departments of Chemistry and hardy@chem.umass.edu.
Jeanne A
JA
Hardy
D053178:Caspase 6 / Q000737:chemistry / Q000378:metabolism*; D053179:Caspase 7 / Q000737:chemistry / Q000378:metabolism; D004795:Enzyme Stability; D006801:Humans; D056004:Molecular Dynamics Simulation; D011485:Protein Binding; D011487:Protein Conformation; D000072756:Protein Conformation, alpha-Helical; D011522:Protons
D011522:Protons; D053178:Caspase 6; D053179:Caspase 7
apoptosis; cysteine protease; hydrogen exchange mass spectrometry; molecular dynamics; neurodegeneration