Lessons on protein structure from interleukin-4: All disulfides are not created equal.

Interleukin-4 (IL-4) is a hematopoietic cytokine composed by a four-helix bundle stabilized by an antiparallel beta-sheet and three disulfide bonds: Cys3-Cys127, Cys24-Cys65, and Cys46-Cys99. IL-4 is involved in several immune responses associated to infection, allergy, autoimmunity, and cancer. Besides its physiological relevance, IL-4 is often used as a "model" for protein design and engineering.

A structural model of an amyloid protofilament of transthyretin.

A docking-and-alignment protocol was devised in order to build amyloid protofilaments of Transthyretin (TTR), starting from partially disrupted TTR monomeric subunits and based on experimentally available information. The docking approach is driven by a combination of shape complementarity and energetic criteria, and uses constraints derived from experimental data obtained for the fibrillar state. The dimeric structures obtained were then subjected to an alignment scheme followed by clustering analysis, producing a collection of protofilaments with distinct geometric properties.