The functions of intrinsically disordered proteins (IDPs) are governed by relationships between information encoded in their amino acid sequences and the ensembles of conformations that they sample as autonomous units. Most IDPs are polyampholytes, with sequences that include both positively and negatively charged residues. Accordingly, we focus here on the sequenceensemble relationships of polyampholytic IDPs. The fraction of charged residues discriminates between weak and strong polyampholytes. Using atomistic simulations, we show that weak polyampholytes form globules, whereas the conformational preferences of strong polyampholytes are determined by a combination of fraction of charged residues values and the linear sequence distributions of oppositely charged residues. We quantify the latter using a patterning parameter κ that lies between zero and one. The value of κ is low for well-mixed sequences, and in these sequences, intrachain electrostatic repulsions and attractions are counterbalanced, leading to the unmasking of preferences for conformations that resemble either self-avoiding random walks or generic Flory random coils. Segregation of oppositely charged residues within linear sequences leads to high κ-values and preferences for hairpin-like conformations caused by long-range electrostatic attractions induced by conformational fluctuations. We propose a scaling theory to explain the sequence-encoded conformational properties of strong polyampholytes. We show that naturally occurring strong polyampholytes have low κ-values, and this feature implies a selection for random coil ensembles. The design of sequences with different κ-values demonstrably alters the conformational preferences of polyampholytic IDPs, and this ability could become a useful tool for enabling direct inquiries into connections between sequence-ensemble relationships and functions of IDPs. I ntrinsically disordered proteins (IDPs) feature prominently in proteins associated with transcriptional regulation and signal transduction (1, 2). IDPs fail to fold autonomously, their sequences are deficient in hydrophobic groups and enriched in polar and charged residues (3), and the thermodynamics and kinetics of coupled folding and binding are linked to the intrinsic conformational properties of IDPs (4-12).IDP sequences include both types of charges, and at least 75% of known IDPs are polyampholytes (13). Coarse-grain parameters that are relevant for describing polyampholytes include the fraction of charged residues (FCR) and net charge per residue (NCPR), which are defined as FCR = (f + + f − ) and NCPR = j f + − f − j, where f + and f − denote the fractions of positive and negatively charges, respectively. Polyampholytes are either strong (FCR ≥ 0.3) or weak (FCR < 0.3) and can be neutral (NCPR ∼ 0) or have a net charge. Single molecule measurements have been used to measure the dimensions of three different polyampholytic systems (8), and a mean field model (14) that requires only FCR, NCPR, and the Debye length as inputs was successful...

Intrinsically disordered proteins (IDPs) showcase the importance of conformational plasticity and heterogeneity in protein function. We summarize recent advances that connect information encoded in IDP sequences to their conformational properties and functions. We focus on insights obtained through a combination of atomistic simulations and biophysical measurements that are synthesized into a coherent framework using polymer physics theories.

Intrinsically disordered proteins and regions (IDPs) represent a large class of proteins that are defined by conformational heterogeneity and lack of persistent tertiary/secondary structure. IDPs play important roles in a range of biological functions, and their dysregulation is central to numerous diseases, including neurodegeneration and cancer. The conformational ensembles of IDPs are encoded by their amino acid sequences. Here, we present two computational tools that are designed to enable rapid and high-throughput analyses of a wide range of physicochemical properties encoded by IDP sequences. The first, CIDER, is a user-friendly webserver that enables rapid analysis of IDP sequences. The second, localCIDER, is a high-performance software package that enables a wide range of analyses relevant to IDP sequences. In addition to introducing the two packages, we demonstrate the utility of these resources using examples where sequence analysis offers biophysical insights.

Transcriptional activation domains are essential for gene regulation, but their intrinsic disorder and low primary sequence conservation have made it difficult to identify the amino acid composition features that underlie their activity. Here, we describe a rational mutagenesis scheme that deconvolves the function of four activation domain sequence features-acidity, hydrophobicity, intrinsic disorder, and short linear motifs-by quantifying the activity of thousands of variants in vivo and simulating their conformational ensembles using an all-atom Monte Carlo approach. Our results with a canonical activation domain from the Saccharomyces cerevisiae transcription factor Gcn4 reconcile existing observations into a unified model of its function: the intrinsic disorder and acidic residues keep two hydrophobic motifs from driving collapse. Instead, the most-active variants keep their aromatic residues exposed to the solvent. Our results illustrate how the function of intrinsically disordered proteins can be revealed by high-throughput rational mutagenesis.

Peptide motifs embedded within intrinsically disordered regions (IDRs) of proteins are often the sites of posttranslational modifications that control cell-signaling pathways. How do IDR sequences modulate the functionalities of motifs? We answer this question using the polyampholytic C-terminal IDR of the cell cycle inhibitory protein p27Kip1 (p27). Phosphorylation of Thr-187 (T187) within the p27 IDR controls entry into S phase of the cell division cycle. Additionally, the conformational properties of polyampholytic sequences are predicted to be influenced by the linear patterning of oppositely charged residues. Therefore, we designed sequence variants of the p27 IDR to alter charge patterning outside the primary substrate motif containing T187. Computer simulations and biophysical measurements confirm predictions regarding the impact of charge patterning on the global dimensions of IDRs. Through functional studies, we uncover cryptic sequence features within the p27 IDR that influence the efficiency of T187 phosphorylation. Specifically, we find a positive correlation between T187 phosphorylation efficiency and the weighted net charge per residue of an auxiliary motif. We also find that accumulation of positive charges within the auxiliary motif can diminish the efficiency of T187 phosphorylation because this increases the likelihood of long-range intra-IDR interactions that involve both the primary and auxiliary motifs and inhibit their contributions to function. Importantly, our findings suggest that the cryptic sequence features of the WT p27 IDR negatively regulate T187 phosphorylation signaling. Our approaches provide a generalizable strategy for uncovering the influence of sequence contexts on the functionalities of primary motifs in other IDRs.p27 | motif | disordered regions