The ABBA Motif Binds APC/C Activators and Is Shared by APC/C Substrates and Regulators

Abstract

The anaphase-promoting complex or cyclosome (APC/C) is the ubiquitin ligase that regulates mitosis by targeting specific proteins for degradation at specific times under the control of the spindle assembly checkpoint (SAC). How the APC/C recognizes its different substrates is a key problem in the control of cell division. Here, we have identified the ABBA motif in cyclin A, BUBR1, BUB1, and Acm1, and we show that it binds to the APC/C coactivator CDC20. The ABBA motif in cyclin A is required for its proper degradation in prometaphase through competing with BUBR1 for the same site on CDC20. Moreover, the ABBA motifs in BUBR1 and BUB1 are necessary for the SAC to work at full strength and to recruit CDC20 to kinetochores. Thus, we have identified a conserved motif integral to the proper control of mitosis that connects APC/C substrate recognition with the SAC.

Dissecting the roles of human BUB1 in the spindle assembly checkpoint

“…Thus, the A-boxcontaining segment, as well as BUBR1, was required for the ability of BUB1 to recruit CDC20. This agrees with a recent study by the Pines laboratory, published while our manuscript was under revision, which shows that recruitment of CDC20 to kinetochores requires the A-box-like motifs (referred to as the ABBA motif in that study) of both BUB1 and BUBR1 (Di Fiore et al, 2015). To retain consistency in nomenclature, we will hereafter refer to the A-boxlike motif in BUB1 as the ABBA motif.…”

“…To retain consistency in nomenclature, we will hereafter refer to the A-boxlike motif in BUB1 as the ABBA motif. Although direct (Di Fiore et al, 2015), the BUB1-CDC20 interaction might be transient because CDC20 peptides were not detected in BUB1 immunoprecipitations by using mass spectrometry (Fig. 4).…”

Structure of an intermediate conformer of the spindle checkpoint protein Mad2

“…1A) (19,(23)(24)(25). Cdc20 and BubR1-Bub3 are also recruited to unattached kinetochores through other mechanisms (26,27). The close proximity of I-Mad2 and Cdc20 stimulates efficient formation of the C-Mad2-Cdc20 complex, which can then associate with BubR1-Bub3 to form MCC (28).…”

Bub1/BubR1: swiss army knives at kinetochores

“…3,5,6 The role of the BubR1 ABBA motif appears to be dual in that it also contributes to SAC silencing by an unknown mechanism. 5 As part of the MCC, BubR1 binds stably to a Cdc20 molecule through its N-terminus so one possibility is that the ABBA motif weakens this interaction to allow efficient MCC disassembly upon checkpoint satisfaction.…”

“…The ABBA motif in Bub1 is required for a functional checkpoint and recruits a pool of Cdc20 to kinetochores. 3,4 Potentially the proximity of Cdc20 to the Mad1-Mad2 complex, coordinated by Bub1, facilitates the binding of Mad2 to Cdc20 the ratelimiting step in MCC formation.…”