allhelical

Allhelical is a descriptive term used in structural biology to refer to protein folds and domains whose secondary structure is predominantly alpha helices. In contrast to all-beta or mixed alpha/beta folds, allhelical architectures are composed largely of helical segments stabilized by hydrophobic interactions and salt bridges.

Common allhelical motifs include four-helix bundles, helix-turn-helix domains, and coiled-coil structures. Helical bundles can form globular cores or elongated fibrous assemblies. Many membrane proteins also feature multiple amphipathic alpha helices that span lipid bilayers, contributing to the allhelical character of those regions.

Allhelical proteins are widespread across life and contribute to diverse functions, including scaffolding, signaling, transcriptional regulation, and enzymatic activity. Their regular geometry often facilitates protein engineering and design because helices are relatively predictable in sequence-structure relationships.

In structural classifications such as SCOP and CATH, allalpha or all-helical architectures are recognized as distinct classes, highlighting their evolutionary and functional diversity. Modern methods combine experimental data with computational predictions to identify allhelical content and to model novel allhelical folds.

Limitations exist, as some proteins classified as allhelical have short non-helical segments; accurate determination of secondary structure can depend on experimental conditions. Nevertheless, the allhelical concept remains a useful framework for describing a major class of protein architecture.