The Vertebrate Mitotic Checkpoint Protein BUBR1 Is an Unusual Pseudokinase

Abstract

Chromosomal stability is safeguarded by a mitotic checkpoint, of which BUB1 and Mad3/BUBR1 are core components. These paralogs have similar, but not identical, domain organization. We show that Mad3/BUBR1 and BUB1 paralogous pairs arose by nine independent gene duplications throughout evolution, followed by parallel subfunctionalization in which preservation of the ancestral, amino-terminal KEN box or kinase domain was mutually exclusive. In one exception, vertebrate BUBR1-defined by the KEN box-preserved the kinase domain but allowed nonconserved degeneration of catalytic motifs. Although BUBR1 evolved to a typical pseudokinase in some vertebrates, it retained the catalytic triad in humans. However, we show that putative catalysis by human BUBR1 is dispensable for error-free chromosome segregation. Instead, residues that interact with ATP in conventional kinases are essential for conformational stability in BUBR1. We propose that parallel evolution of BUBR1 orthologs rendered its kinase function dispensable in vertebrates, producing an unusual, triad-containing pseudokinase.

Mammalian Myosin-18A, a Highly Divergent Myosin

“…However, a triad of critically conserved consensus residues remains unperturbed in this inactive kinase. Mutation of one of these residues results in phenotypes in cells (10,11), but the paper by Suijkerbuijk et al (63) shows that this is probably due to a reduced conformation stability of the protein and not to elimination of kinase activity (because such activity never existed), as suggested by the authors of the papers. Similarly with mammalian myosin-18A, many of the amino acids important for ATP hydrolysis in the myosin consensus sequences have been replaced with ones that would not be able to carry out the same function, but the two residues mutated in the aforementioned papers still adhere to the consensus sequence for the P-loop.…”

“…This raises the question of how one "inactivates" an already inactive protein. In this regard, it is interesting to note a recent study by Suijkerbuijk et al (63) of BUBR1, a pseudokinase involved in a mitotic checkpoint. BUBR1 shares significant similarity to known kinases in terms of both sequence and protein domain architecture, but many residues known to be critical for enzymatic activity have been replaced during evolution, rendering it inactive as a kinase.…”

Dawn of the dead: protein pseudokinases signal new adventures in cell biology

“…However, several domains that contain apparently conventional protein kinase catalytic residues, such as Ror1 [41,42], RYK [7,43] and BubR1 [44], appear to be catalytically inactive in vitro. Although clearly a functional, rather than bioinformatic, definition, we believe that these domains should logically be grouped with the human pseudokinases ( Figure 1).…”

The molecular basis for kinesin functional specificity during mitosis

“…In addition, the recruitment of a phosphatase such as PP1 to kinetochore-targeted motors can fine-tune the activity of these motors by opposing Aurora B and Plk1 activity as tension is established [Liu et al, 2010]. At kinetochores, CENP-E has also been proposed to act as a “cyclin” for BubR1 kinase activity, [Mao et al, 2003; Weaver et al, 2003; Mao et al, 2005] although whether BubR1 has kinase activity that is required for mitosis is debated [Suijkerbuijk et al, 2012; Elowe, 2011]. In total, processive kinesins may use their unique non-motor domains to act as an interaction platform and recruit molecules to a particular structure to drive mitotic progression.…”