Polyglutamine Solution-State Structural Propensity Is Repeat Length Dependent

Reviewing the Structure-Function Paradigm in Polyglutamine Disorders: A Synergistic Perspective on Theoretical and Experimental Approaches

Polyglutamine (polyQ) disorders are a group of neurodegenerative diseases characterized by the excessive expansion of CAG (cytosine, adenine, guanine) repeats within host proteins. The quest to unravel the complex diseases mechanism has led researchers to adopt both theoretical and experimental methods, each offering unique insights into the underlying pathogenesis. This review emphasizes the significance of combining multiple approaches in the study of polyQ disorders, focusing on the structure-function correlations and the relevance of polyQ-related protein dynamics in neurodegeneration. By integrating computational/theoretical predictions with experimental observations, one can establish robust structure-function correlations, aiding in the identification of key molecular targets for therapeutic interventions. PolyQ proteins' dynamics, influenced by their length and interactions with other molecular partners, play a pivotal role in the polyQ-related pathogenic cascade. Moreover, conformational dynamics of polyQ proteins can trigger aggregation, leading to toxic assembles that hinder proper cellular homeostasis. Understanding these intricacies offers new avenues for therapeutic strategies by fine-tuning polyQ kinetics, in order to prevent and control disease progression. Last but not least, this review highlights the importance of integrating multidisciplinary efforts to advancing research in this field, bringing us closer to the ultimate goal of finding effective treatments against polyQ disorders.

A Model for Inhomogeneously Broadened Raman Bands

Detailed information on the physics and chemistry of a sample can be derived from Raman band parameters. However, the Raman band observed by the detector contains artifacts from the instrument, complicating analysis of these details. To obtain Raman data that can be directly correlated to sample properties and to compare Raman spectra across instrumentation, instrumental effects must be accounted for. This is commonly performed for homogeneously broadened bands by determining the contribution of the slit function to the spectrum. However, there is currently no method for understanding instrumental effects on inhomogeneously broadened bands or a method to account for these effects when examining data and comparing data across instruments, though these analyses are commonplace. This shortfall injects an unknown error into the analyses and comparisons of inhomogeneously broadened Raman bands. This work derives a method of modeling inhomogeneous Raman bands as a continuum of homogeneous Raman bands spanning the width of the stochastic fluctuation energy well that causes inhomogeneous broadening. This model is combined with previous work to examine the effects of the slit function, intrinsic Raman band, stochastic energy well, homogeneously broadened Raman band, and slit width band parameters on the inhomogeneously broadened Raman band parameters. This model, for the first time, provides a quantitative description of the experimental parameters that effect the inhomogeneous Raman bands.

Stabilization of elongated polyglutamine tracts by a helical peptide derived from N-terminal huntingtin

In Huntington's disease, the length of the polyglutamine tract in the mutant protein correlates positively with the formation of aggregates and disease symptoms and severity of the disease. Some disease-modifying factors exist. However, no organized study has been carried out to investigate the effect of polyglutamine length in the mutant protein on the efficacy of a therapeutic strategy. We had shown earlier that the helical peptide arising out of the N-terminal stretch of normal huntingtin is able to inhibit aggregation of a number of proteins, including luciferase, α-synuclein, p53, and Rnq1. In this work, we show that polyglutamine stretches of differing lengths, namely 51Q, 72Q, and 103Q, form a mixture of aggregates at different rates, with the rate increasing in a polyQ length-dependent manner. The helical peptide is able to inhibit the rate of aggregation. The extent of inhibition was different when measuring either total aggregation or only fibrillar aggregates, suggesting that the helical peptide with benign polyQ stretch alters the aggregation landscape of different elongated polyQ lengths differently. Our results suggest that designing a therapeutic approach to inhibit protein aggregation must take note of polyQ length of the protein.