A return to chemotaxis

We can briefly return, at this point, to chemotaxis - since we are now in a better position to understand it. In the case of neutrophils, a similar signalling process will take place in response to chemotactic factors binding to ligands on the cell surface. The process isn't well-understood, but in the case of chemotaxis I believe that G protein-coupled receptors (GPCRs) are used, rather than toll-like receptors. The principles are very much the same, however. In this case, signalling is initially effected by a class of protein called G proteins (or guanosine nucleotide-binding proteins). When unactivated, these proteins are bound to the GPCRs. When a ligand binds to the GPCR, it brings about a conformational change, which leads to the activation of the G protein. This is a very cursory overview and the way it is done is not fully understood, but we should be aware that there are a number of steps which I am not treating here. Ultimately, however, the activated G protein can then take part in chemical reactions such as those described earlier, which results in the polymerisation of actin filaments and, finally, a pseudopod.