Abstract
AAA ATPases form a functionally diverse superfamily of proteins. Most members form homo-hexameric ring complexes, are catalytically active only in the fully assembled state, and show co-operativity among the six subunits. The mutual dependence among the subunits is clearly evidenced by the fact that incorporation of mutated, inactive subunits can decrease the activity of the remaining wild type subunits. For the first time, we develop here models to describe this form of allostery, evaluate them in a simulation study, and test them on experimental data. We show that it is important to consider the assembly reactions in the kinetic model, and to define a formal inhibition scheme. We simulate three inhibition scenarios explicitly, and demonstrate that they result in differing outcomes. Finally, we deduce fitting formulas, and test them on real and simulated data. A non-competitive inhibition formula fitted experimental and simulated data best. To our knowledge, our study is the first one that derives and tests formal allosteric schemes to explain the inhibitory effects of mutant subunits on oligomeric enzymes.
Highlights
Expression from Two Alleles Enzymes often work in oligomeric assemblies with multiple, interacting subunits
To interpret the inhibition pattern of mixtures of wild type and mutated spastin we first show that the assembly pathway kinetics of hexameric rings is an important determinant for the steady state ATPase turnover, before we investigate alternative allosteric schemes that can explain experimental observations
The evidence that hexamers still are the active form of the enzyme are indirect. (i) Inhibition studies show that the addition of inactive mutants to wild type spastin slows down the ATP turnover per wild type subunit [16]. (ii) structural investigations of mutant protein and analogies to other AAA ATPases indicate that spastin forms hexameric ring structures that probably represent the active form of the enzyme [5,15,16,31,32]
Summary
Expression from Two Alleles Enzymes often work in oligomeric assemblies with multiple, interacting subunits. For most (but not all) human genes the expression levels of the two alleles are similar, and no allele-specific expression is found [1] For this majority of cases, oligomeric enzymes are composed of proteins expressed from different alleles. In normal cases, this does not have any consequences for the organism because both alleles are very similar and usually both functional. There are several mechanisms that can lead to dominantnegative inheritance among them haplo-insufficiency, aggregation of the mutated gene product, complex genetic feedback circles we focus here on cases where the gene products of the intact and the defective allele co-assemble into a protein complex, and the mutant gene product inhibits the proper function of the wild type gene product
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
