Intrinsically Disordered Regions in Autophagy Proteins

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DESCRIPTION (provided by applicant): Autophagy is responsible for the vesicular sequestration and lysosomal degradation of unwanted, damaged or harmful macromolecular cytoplasmic components, resulting in nutrient recycling. Thus, autophagy plays an important role in a wide range of organismal homeostasis processes including life-span extension, embryonic development, tissue-differentiation, cell-growth, surviving environmental stress conditions like starvation, high temperatures and hypoxia as well as internal stressors like damaged organelles, mutant proteins, free radicals and intracellular pathogens. Defects in autophagy are implicated in many disorders such as reduced life-span, neurodegenerative and muscular disorders, age-weakened immunity against infectious diseases; hence, elucidating the structure-based mechanism of autophagy proteins is essential to understanding these diseases and devising potential therapeutics targeting them. Intrinsically disordered regions (IDRs), i.e. regions that lack ordered secondary and tertiary structure, are common, yet poorly understood, features of many proteins. Mutations implicated in important diseases like neurodegenerative disorders like Alzheimer's disease often map to IDRs. Our bioinformatics analysis shows that IDRs are a predominant feature of autophagy proteins. We experimentally verify structural disorder in a selected subset of autophagy protein IDRs, including a large IDR within the conserved autophagy effector, Beclin 1, an essential component of the autophagy nucleation complex. Further, based on the results of a bioinformatics analyses to investigate the potential biological function of IDRs in mediating protein interactions, we experimentally investigate selected binding motifs predicted within selected IDRs, as well as conformational transitions in these IDRs, with a special focus on the Beclin 1 IDR. Further, we have identified several prospective protein interactions of the Beclin 1 IDR, and these will be experimentally validated. Beclin 1 is directly implicated in many human diseases. Reduced Beclin 1 levels are associated with decreased longevity and an elevated risk of age-related disorders like Alzheimer's disease; while an increase in Beclin 1-mediated autophagy, such as by caloric restriction, increases cellular and organismal life span. Beclin 1 appears to be a protein interaction hub for autophagy as it is implicated in interactions with at least 20 other cellular proteins. The work in this propsal will lay the groundwork for future research building a detailed structural and mechanistic understanding of these interactions that will elucidate how these interactions compete with or complement each other to regulate Beclin 1-mediated autophagy, the role of disruptions of these interactions in human diseases and potential therapeutics that target the Beclin 1 IDR or its interactions.