Phosphorylation site analysis of the centrosomal Nek2 kinase and its substrates
The duplication and separation of centrosomes is controlled in large part by protein phosphorylation. Nek2 is a protein kinase that localises to the centrosomes and has peak activity at the onset of mitosis. The aim of this thesis was to determine how the Nek2 protein is regulated and to identify phosphorylation sites both within the Nek2 kinase and its centrosomal substrates. Identification of a Nek2 phosphorylation concensus sequence should also facilitate the discovery of novel Nek2 substrates. Here, we have mapped eleven Nek2 autophosphorylation sites and identified those which are critical for Nek2 activity. These include sites within the activation loop of the catalytic domain and in the C-terminal non-catalytic domain. We have also identified a region within the Nek2 protein that may act as an auto-inhibitory domain. We also identify Nek2 phosphorylation sites within the centrosomal proteins, N1p and C-Nap1. N1p is localised to the mother centriole and may act as a novel microtubule anchoring protein. We have demonstrated that the localisation of N1p is dependent upon the Nek2 protein kinase. Others have previously identified P1k1 as a kinase involved in N1p regulation and we demonstrate here that Nek2 acts upstream of P1k1 and may be a P1k1 priming kinase. In addition, we identify Cdk1 as a possible P1k1 priming kinase on N1p. C-Nap1 is a protein involved in centriole cohesion and phosphorylation by Nek2 may regulate its interaction with other centriole linker proteins. This work substantially increases our knowledge of Nek2 regulation by phosphorylation and also extends our understanding of how it regulates centrosomes structure and function in a cell cycle dependent manner.