Designs on a curve

Symmetry and Dissymmetry in Protein Structure—System-Coding Its Biological Specificity

The solenoid is a highly ordered structure observed in proteins, characterized by a set of symmetries. A group of enzymes—lyases containing solenoid fragments—was subjected to analysis with focus on their distribution of hydrophobicity/hydrophilicity, applying the fuzzy oil drop model. The model differentiates between a monocentric distribution hydrophobic core (spherical symmetry—mathematically modeled by a 3D Gaussian) and linear propagation of hydrophobicity (symmetry based on translation of structural units, i.e., chains—evident in amyloids). The linearly ordered solenoid carries information that affects the structure of the aqueous solvent in its neighborhood. Progressive disruption of its symmetry (via incorporation of asymmetrical fragments of varying size) appears to facilitate selective interaction with the intended substrate during enzymatic catalysis.

Establishment of the early cilia preassembly protein complex during motile ciliogenesis

Motile cilia are characterized by dynein motor units, which preassemble in the cytoplasm before trafficking into the cilia. Proteins required for dynein preassembly were discovered by finding human mutations that result in absent ciliary motors, but little is known about their expression, function, or interactions. By monitoring ciliogenesis in primary airway epithelial cells and MCIDAS-regulated induced pluripotent stem cells, we uncovered two phases of expression of preassembly proteins. An early phase, composed of HEATR2, SPAG1, and DNAAF2, preceded other preassembly proteins and was independent of MCIDAS regulation. The early preassembly proteins colocalized within perinuclear foci that also contained dynein arm proteins. These proteins also interacted based on immunoprecipitation and Förster resonance energy transfer (FRET) studies. FRET analysis of HEAT domain deletions and human mutations showed that HEATR2 interacted with itself and SPAG1 at multiple HEAT domains, while DNAAF2 interacted with SPAG1. Human mutations in HEATR2 did not affect this interaction, but triggered the formation of p62/Sequestosome-1-positive aggregates containing the early preassembly proteins, suggesting that degradation of an early preassembly complex is responsible for disease and pointing to key regions required for HEATR2 scaffold stability. We speculate that HEATR2 is an early scaffold for the initiation of dynein complex assembly in motile cilia.

Revealing aperiodic aspects of solenoid proteins from sequence information

MOTIVATION

Repeat proteins, which contain multiple repeats of short sequence motifs, form a large but seldom-studied group of proteins. Methods focusing on the analysis of 3D structures of such proteins identified many subtle effects in length distribution of individual motifs that are important for their functions. However, similar analysis was yet not applied to the vast majority of repeat proteins with unknown 3D structures, mostly because of the extreme diversity of the underlying motifs and the resulting difficulty to detect those.

RESULTS

We developed FAIT, a sequence-based algorithm for the precise assignment of individual repeats in repeat proteins and introduced a framework to classify and compare aperiodicity patterns for large protein families. FAIT extracts repeat positions by post-processing FFAS alignment matrices with image processing methods. On examples of proteins with Leucine Rich Repeat (LRR) domains and other solenoids like proteins, we show that the automated analysis with FAIT correctly identifies exact lengths of individual repeats based entirely on sequence information.

AVAILABILITY AND IMPLEMENTATION

https://github.com/GodzikLab/FAIT CONTACT: adam@godziklab.org

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Identification of repetitive units in protein structures with ReUPred

Over the last decade, numerous studies have demonstrated the fundamental importance of tandem repeat (TR) proteins in many biological processes. A plethora of new repeat structures have also been solved. The recently published RepeatsDB provides information on TR proteins. However, a detailed structural characterization of repetitive elements is largely missing, as repeat unit annotation is manually curated and currently covers only 3 % of the bona fide TR proteins. Repeat Protein Unit Predictor (ReUPred) is a novel method for the fast automatic prediction of repeat units and repeat classification using an extensive Structure Repeat Unit Library (SRUL) derived from RepeatsDB. ReUPred uses an iterative structural search against the SRUL to find repetitive units. On a test set of solenoid proteins, ReUPred is able to correctly detect 92 % of the proteins. Unlike previous methods, it is also able to correctly classify solenoid repeats in 89 % of cases. It also outperforms two recent state-of-the-art methods for the repeat unit identification problem. The accurate prediction of repeat units increases the number of annotated repeat units by an order of magnitude compared to the sequence-based Pfam classification. ReUPred is implemented in Python for Linux and freely available from the URL: http://protein.bio.unipd.it/reupred/ .

Restricted mobility of side chains on concave surfaces of solenoid proteins may impart heightened potential for intermolecular interactions

Significant progress has been made in the determination of the protein structures with their number today passing over a hundred thousand structures. The next challenge is the understanding and prediction of protein-protein and protein-ligand interactions. In this work we address this problem by analyzing curved solenoid proteins. Many of these proteins are considered as "hub molecules" for their high potential to interact with many different molecules and to be a scaffold for multisubunit protein machineries. Our analysis of these structures through molecular dynamics simulations reveals that the mobility of the side-chains on the concave surfaces of the solenoids is lower than on the convex ones. This result provides an explanation to the observed preferential binding of the ligands, including small and flexible ligands, to the concave surface of the curved solenoid proteins. The relationship between the landscapes and dynamic properties of the protein surfaces can be further generalized to the other types of protein structures and eventually used in the computer algorithms, allowing prediction of protein-ligand interactions by analysis of protein surfaces.