Pentaxins

Pentaxins are a family of soluble, multimeric proteins characterized by a conserved pentaxin fold. This fold consists of a beta-sheet core surrounded by alpha-helices, which assemble into cyclic pentameric structures. These pentamers can further associate to form higher-order structures, such as hexameric dimers. The pentaxin domain is approximately 150 amino acids long.

A hallmark of pentaxins is the presence of a conserved pentameric ring formed by five identical subunits. This structure is crucial for their ability to bind to a variety of ligands. The binding sites are typically located on the surface of the pentamer, often in a calcium-dependent manner. Pentaxins are found across a wide range of species, from invertebrates to vertebrates, suggesting an ancient evolutionary origin and diverse biological roles.

The functions of pentaxins are multifaceted and often involve the innate immune system. Many pentaxins act as pattern recognition molecules, binding to conserved molecular structures on the surface of pathogens, such as bacterial lipopolysaccharides or viral nucleic acids. This binding can facilitate pathogen clearance through opsonization, a process where the pentaxin marks the pathogen for uptake by phagocytic cells. Some pentaxins also exhibit anti-inflammatory and immunomodulatory properties, influencing the activity of other immune cells. Their roles extend beyond immunity, with some pentaxins implicated in processes like tissue repair, angiogenesis, and cell proliferation. Examples include C-reactive protein (CRP) in humans, serum amyloid P component (SAP), and pentraxin 3 (PTX3).