BBB seminar: Terje Johansen

Terje Johansen
Head of the Molecular Biology Research Group, Department of Biochemistry, Institute of Medical Biology, University of Tromsø, Norway (http://www.fagmed.uit.no/info/imb/biokjemi/molbio/)

The Phox and Bem1p (PB1) domain constitutes a recently recognized protein-protein interaction domain found in the atypical protein kinase C (aPKC) isoenzymes, / - and PKC; members of mitogen-activated protein kinase (MAPK) modules like MEK5, MEKK2, and MEKK3; and in several scaffold proteins involved in cellular signaling. Among the last group, p62 and Par6 are involved in coupling the aPKCs to signaling pathways involved in cell survival, growth control, and cell polarity. By mutation analyses and molecular modeling, we have identified critical residues at the interaction surfaces of the PB1 domains of aPKCs and p62. We have also determined the abilities of mammalian PB1 domain proteins to form heteromeric and homomeric complexes mediated by this domain. We report several novel interactions within this family of proteins.

The p62 protein forms circular bodies or speckles, termed sequestosomes, in the cytosol of cells. In patients with neurodegenerative diseases characterized by ubiquitin-containing aggregates, or inclusions, p62 is also present in these aggregates. p62 contains a C-terminal poly-ubiquitin-binding UBA domain in addition to the N-terminal PB1 domain. We show that the PB1 and UBA domains are both involved in forming these bodies.