#11573 adustment to GO:0033597 mitotic checkpoint complex plus new subcomplex GO:1990706 MAD1 complex

[Birgit Meldal]

Hi Tanya,

I have just created GO:1990706 MAD1 complex in TG FF which is a subcomplex or feeder complex for the MCC. It appears that the MAD1 protein should be part of the MCC, so we need at least a small tweak to the def of GO:0033597 mitotic checkpoint complex. What I'm not entirely sure of is whether the MAD1 dimer takes part in the MCC or if it's just one MAD1 protomer. The dimer certainly appears to exist initially as the different kinetochore complexes get assembled.

IF the dimer is part of the MCC we need to add the part_of relationship.

PMIDs: 22493223, 22898774

Birgit

[Valerie Wood]

Hi Birgit,

Although Mad1 is a MCC binding partner, is it a bona vida complex member? I’m not sure that it is in yeast, although it anchors the complex to the nuclear membrane
and regulates its entry into the nucleus....

Val

[Valerie Wood]

The intro to the paper I am curating (11950879) says

Mad2 forms protein complexes with other components of the spindle checkpoint. The Mad1-Mad2 complex, which exists throughout the cell cycle (Chen et al., 1999), is necessary for localization of Mad2 on unattached kinetochores (Chen et al., 1998). Mad2 also forms a complex with Mad3 in budding yeast (Hardwick et al., 2000). Because the Mad2-Mad3 complex also contains Cdc20, this complex may function at the endpoint of the checkpoint signaling cascade.

I think these are possibly independent complexes...

[Valerie Wood]

Ignore previous, I think it likely is a true member....

[Birgit Meldal]

No worries, Val! This complex was curated by a short-term project student so I'm dealing with the GO annotation requests myself. It took me a moment as well to be convinced of it's membership :)

Birgit

[Valerie Wood]

I think I previously thought this was involved in a preceding localization step, but now I realise it is involved in the localization of MCC to unattached kinetochores when MCC is active.
v

[Tanya Berardini]

MAD1 complex part_of MCC

or

MCC has_part MAD1 complex
?

Change:

A multiprotein complex that functions as a mitotic checkpoint inhibitor of the anaphase-promoting complex/cyclosome (APC/C). In budding yeast this complex consists of Mad2p, Mad3p, Bub3p and Cdc20p, and in mammalian cells it consists of MAD2, BUBR1, BUB3, and CDC20.

To:

??

[Birgit Meldal]

We found another paper: PMID:18022367 (MAD2 dimer crystal structure)

From the introduction:
"Kinetochores devoid of microtubules retain a tight complex of Mad2 with another SAC protein named Mad1 (Chen et al., 1999, Chen et al., 1998, Chung and Chen, 2002, De Antoni et al., 2005a, Luo et al., 2002, Martin-Lluesma et al., 2002, Nasmyth, 2005, Sironi et al., 2002 and Vink et al., 2006). The way in which Mad1 binds Mad2 is equivalent to that of Cdc20, in that Mad1 binds to the same ligand-binding site of C-Mad2. There is now substantial evidence that the tight Mad1–Mad2 complex, which is further stabilized by 2:2 tetramerization, does not significantly dissociate during checkpoint activation (De Antoni et al., 2005a, Shah et al., 2004 and Vink et al., 2006). Its function at the kinetochore is to recruit from the mitotic cytosol a different conformer of Mad2, known as O-Mad2 (or N1 Mad2), for Cdc20 binding (De Antoni et al., 2005a and Vink et al., 2006). [...] The logic of this network is that the conformational dimerization of O-Mad2 with Mad1-bound C-Mad2 facilitates the complex conformational rearrangement required to bind Cdc20, possibly through the creation of a structural intermediate (Figure S1 in the Supplemental Data available with this article online). This model is named “Mad2 template” model, as it suggests that C-Mad2 bound to Mad1 acts as a template to generate C-Mad2 bound to Cdc20 (De Antoni et al., 2005a, Nasmyth, 2005 and Yu, 2006)."

Also see Fig 1 in PMID:22898774 (review)

So, now we think MAD1 dimer recruits 2 units of C-MAD2 to form a 2:2 tetramer. The latter then recruits 2x O-MAD2 before releasing C-MAD2 to form MCC (with its other subunits). Some re-conformation appears to happen in this hexamer but details are scant.

Hence, MAD1 is NOT part of MCC after all but assists in it's assembly by providing the correctly conformed version of C-MAD2 for the MCC.

Hope that doesn't confuse the issue too much :)
I think it also means we can close this ticket (unless Val has more insightful comments :) )

Birgit

[Valerie Wood]

Do the 2 mad2 containing complexes have totally different roles ? Mad1 complex to monitor unattached kinetochores and full MCC to sequester Cdc20 and negatively regulate metaphase/anaphase transition?

I had assumed that cdc20 was part of the kinetochore associated complex, but this can't be so if it shares a binding site with mad1...Cdc20 must be sequestered by the MCC in metaphase to prevent chromosome segregation so I guess this version must exist at the same time.

Not insightful, just pondering....

[Birgit Meldal]

Yes, Val.

According to the review paper (22898774, Fig 1) MAD1-MAD2 (C-MAD2 version) complex is bound to the kinetochore, recruits the O-MAD2 units and converts them into C-MAD2 units which then bind CDC20 and associated MCC proteins to form MCC.

C-MAD2 as part of MCC inhibits APC/C activity and arrests the cell cycle until all kinetochores are attached. There appears to be some form of 'intermediate' I-MAD2 on the MAD1-MAD2 complex that aids the conversion of O- to C- form.

Once all kinetochores have been attached, p31 binds MAD2 of the MAD1-MAD2 complex which stops recruitment of MAD2 to MCC, the release of APC/C and allows cell cycle progression.

Birgit

[Birgit Meldal]

PS: I'm having other MAD1 and MAD2 complexes on my annotation list :)

[Valerie Wood]

Thanks for the review, much clearer now! and for the Linked In, now I will recognise you when I am at the EBI.

I am trying to work my way through all of kinetochore/spindle chromosome segregation complexes and publications, but it is a tonne in fission yeast so it is slow....

[Birgit Meldal]

I didn't realise until today that you where in CB! I was in one of the ontology seminars you came to (last year...) but didn't have the chance to say 'Hello'.

Regarding 'all the kinetochore/spindle chromosome segregation complexes', that's a task and a half!

Birgit

[Tanya Berardini]

So...

can we close this issue? (she says, hopefully.)

[Birgit Meldal]

Yes, unless Val objects...

Sorry about the mess, but we've learnt something :)

Birgit

[Tanya Berardini]

I've learned something as well. :) It's good to let these requests simmer for a bit before implementing.

[Valerie Wood]

Yes I'm happy and I learned something too.... Have used in slides for a curation talk tomorrow :)

[Tanya Berardini]

Excellent!