Complete Structure of an Epithelial Keratin Dimer: Implications for Intermediate Filament Assembly

Abstract

Keratins are cytoskeletal proteins that hierarchically arrange into filaments, starting with the dimer sub-unit. They are integral to the structural support of cells, in skin, hair and nails. In skin, keratin is thought to play a critical role in conferring the barrier properties and elasticity of skin. In general, the keratin dimer is broadly described by a tri-domain structure: a head, a central rod and a tail. As yet, no atomistic-scale picture of the entire dimer structure exists; this information is pivotal for establishing molecular-level connections between structure and function in intermediate filament proteins. The roles of the head and tail domains in facilitating keratin filament assembly and function remain as open questions. To address these, we report results of molecular dynamics simulations of the entire epithelial human K1/K10 keratin dimer. Our findings comprise: (1) the first three-dimensional structural models of the complete dimer unit, comprising of the head, rod and tail domains; (2) new insights into the chirality of the rod-domain twist gained from analysis of the full domain structure; (3) evidence for tri-subdomain partitioning in the head and tail domains; and, (4) identification of the residue characteristics that mediate non-covalent contact between the chains in the dimer. Our findings are immediately applicable to other epithelial keratins, such as K8/K18 and K5/K14, and to intermediate filament proteins in general.

The X-Ray Crystal Structure of the Keratin 1-Keratin 10 Helix 2B Heterodimer Reveals Molecular Surface Properties and Biochemical Insights into Human Skin Disease

“…This includes identification of protein-binding partners and the functions of surface pockets, the determination of additional structures of keratins, particularly their higher-order assemblies, and how the head and tail domains interact with the keratin helices in the intact molecule. Recent molecular dynamics simulation of an intact K1-K10 heterodimer model proposed ways in which all domains of a keratin (head, helices, linkers, and tail) relate in 3D space; it further emphasized the need for experimental crystal structures to validate the models (Bray et al, 2015). Future studies must define more clearly how point mutations cause disease – at the heterodimer level and in the KIF aggregate.…”

CCFold: rapid and accurate prediction of coiled-coil structures and application to modelling intermediate filaments

“…The CCFold algorithm brings the modelling of the IF dimer structure to a new level. Past attempts included choosing some starting conformation, based either on the available crystal structures of protein fragments or some rather crude structural assumptions, followed by molecular dynamics (MD) (Chou and Buehler, 2012;Bray et al, 2015). The problem here is that, given the size of the IF dimer and current computational capacities, such MD simulations could never guarantee a convergence to a correct fully energyminimised structure.…”

Epidermolysis bullosa simplex–generalized severe type due to keratin 5 p.Glu477Lys mutation: Genotype‐phenotype correlation and in silico modeling analysis

“…Keratins are heterodimeric proteins composed of a head, central rod domain, and tail region . The central rod domain is comprised of several subunits.…”

“…4 Keratins are heterodimeric proteins composed of a head, central rod domain, and tail region. 5,6 The central rod domain is comprised of several subunits. Two subunits, 1A (or helix initiation peptide, HIP) and 2B (helix termination peptide, HTP), located at the ends of the central rod domain, are crucial for the creation of functional keratin filaments.…”