C5a is a protein fragment released from complement component C5. In humans, the polypeptide contains 74 amino acids but is rapidly metabolised by a serum enzyme, carboxypeptidase B to a 73 amino acid form, C5a des-Arg. C5a is an anaphylatoxin, causing the release of histamine from mast cells; C5a des-Arg is a much less potent anaphylatoxin. However, both forms are effective leucocyte chemoattractants, causing the accumulation of white blood cells, especially neutrophil granulocytes, at sites of complement activation. Ribbon diagram of the enzyme TIM. TIM is catalytically perfect, meaning its conversion rate is limited, or nearly limited to its substrate diffusion rate. ... Anaphylatoxin, or anaphylotoxin, is a fragment (C3a, C4a or C5a) of the complement system that triggers degranulation of (release of substances from) mast cells or basophils, which is an important part of the immune system in all kinds of inflammation and especially as part of defense against parasites. ... Histamine is a biogenic amine chemical involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter. ... A mast cell (or mastocyte) is a resident cell of connective tissue that contains many granules rich in histamine and heparin. ... Granulocytes are a category of white blood cells, characterised by the fact that all types have differently staining granules in their cytoplasm on light microscopy. ...

C5a binds to a receptor protein on the surface of target cells, C5aR or CD88. This is a member of the G-protein-coupled receptor superfamily of proteins, predicted to have seven transmembrane helical domains of largely hydrophobic amino acid residues, forming three intra- and three extra-cellular loops, with an extracellular N-terminus and an intracellular C-terminus. C5a binding to the receptor is a two-stage process: an interaction between basic residues in the helical core of C5a and acidic residues in the extracellular N-terminal domain allows the C-terminus of C5a to bind to residues in the receptor transmembrane domains. The latter interaction leads to receptor activation, and the transduction of the ligand binding signal across the cell plasma membrane to a cytoplasmic G protein. Receptor may refer to: In telecommunication, a receiver. ... The seven transmembrane α-helix structure of a G-protein-coupled receptor. ... An amino acid residue is what is left of an amino acid once a molecule of water has been lost (an H+ from the nitrogenous side and an OH- from the carboxylic side) in the formation of a peptide bond. ... Drawing of a cell membrane A component of every biological cell, the cell membrane (or plasma membrane) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ...