As Reza already pointed out, ITC cannot tell you anything about the sub-processes that underlay an equilibrium, be it complicated like 2A+B2 <-> AB2 + A <-> A2B2, or with (virtually) no intermediate 2A+B2 <-> A2B2 due to a fast second forward reaction , or a simple one-to-one model A+B2 <-> AB2.
Given the lack of additional information, its probably good to assume a simple one-to-one model and titrate either partner to the other. If you have two separate binding steps (with similar Kd for B2 for A as well as AB2 for A), you would measure an apparent affinity and would see the stochiometrics according to the inflection point (be it around equimolar excess or at 0.5 or 2, depending on whether you titrate A or B). If the reaction is more complicated and the the affinities for B2 for A differ significantly much from the affinity of AB2 for A, then a simple one-to-one would leave some notable information in the residual standard deviations (meaning, the residuals would not spread normally around the Regression line, but should show a wavy pattern). Sorry for the long mail.. Matthias Dr. Matthias Barone AG Kuehne, Rational Drug Design Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP) Robert-Rössle-Strasse 10 13125 Berlin Germany Phone: +49 (0)30 94793-284 ________________________________ From: CCP4 bulletin board <[email protected]> on behalf of Michael Fairhead <[email protected]> Sent: Thursday, October 3, 2019 5:59:22 PM To: [email protected] Subject: Re: [ccp4bb] ITC question -dimer vs monomer Hello, If you Google Alan cooper ITC insulin, you should find his work describing the study of insulin dimer:monomer equilibrium and the effect of cyclodextrin studied via ITC. This may be of some help. Cheers Mike https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.chem.gla.ac.uk/staff/alanc/itcdil.pdf&ved=2ahUKEwiOpoeisYDlAhUDThUIHX5mAyMQFjAAegQIAhAB&usg=AOvVaw0Ng-W03upy4DG12unFGDY3 From: CCP4 bulletin board <[email protected]> On Behalf Of Bernhard Rupp Sent: 03 October 2019 16:52 To: [email protected] Subject: Re: [ccp4bb] ITC question -dimer vs monomer I am not looking for anything yet – I wonder what – if any – the consequences of doing it one way or the other would be. I am reasonably certain that any difference affects the analysis. Thx, BR From: CCP4 bulletin board <[email protected]<mailto:[email protected]>> On Behalf Of Keller, Jacob Sent: Thursday, October 3, 2019 17:41 To: [email protected]<mailto:[email protected]> Subject: Re: [ccp4bb] ITC question -dimer vs monomer I don’t understand what you are trying to do—are you trying to show, by the difference in ITC response, that the predictions you made about the oligomerization are true? JPK +++++++++++++++++++++++++++++++++++++++++++++++++ Jacob Pearson Keller Research Scientist / Looger Lab HHMI Janelia Research Campus 19700 Helix Dr, Ashburn, VA 20147 Desk: (571)209-4000 x3159 Cell: (301)592-7004 +++++++++++++++++++++++++++++++++++++++++++++++++ The content of this email is confidential and intended for the recipient specified in message only. It is strictly forbidden to share any part of this message with any third party, without a written consent of the sender. If you received this message by mistake, please reply to this message and follow with its deletion, so that we can ensure such a mistake does not occur in the future. From: CCP4 bulletin board <[email protected]<mailto:[email protected]>> On Behalf Of Bernhard Rupp Sent: Thursday, October 3, 2019 11:06 AM To: [email protected]<mailto:[email protected]> Subject: [ccp4bb] ITC question -dimer vs monomer Hi Fellows, please let me ask the respective experts an ITC question: I have 2 proteins, stable and dialyzed in identical buffer. A is a monomer and B an obligate dimer. I suspect that eventually a A2B2 dimer will form. Intuitively, it should make a difference whether I titrate the dimer with the monomer or vice versa. In the first case, a momomer would initially meet a lot of free dimers, and I would expect that randomly, a AB2 complex is more likely to form than a A2B2 (let’s disregard any more complex colligative/cooperative effects). If I drip the dimer into the monomer pool, it is quite likely that the B dimer meets 2 free As, and I get right away a higher population of A2B2s. Maybe at dilutions of ITC and with sufficient equilibration that is not an issue at all (again, absent any cooperative effects that might alter the first Kd vs. the second, despite the sites on the dimer are at least initially equivalent). Can someone guide me towards literature about this or perhaps share some first-hand experience? Many thanks, BR ------------------------------------------------------ Bernhard Rupp http://www.hofkristallamt.org/<https://urldefense.com/v3/__http:/www.hofkristallamt.org/__;!oCotSwSxbw8!SE9mT6grUy1tHFSKLCraXt4bhlDri03OEMEyqQUCLAVSLsg3vwn0GTQtxbStgtNvxBs$> [email protected]<mailto:[email protected]> +1 925 209 7429 +43 676 571 0536 ------------------------------------------------------ Many plausible ideas vanish at the presence of thought ------------------------------------------------------ ________________________________ To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1<https://urldefense.com/v3/__https:/www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1__;!oCotSwSxbw8!SE9mT6grUy1tHFSKLCraXt4bhlDri03OEMEyqQUCLAVSLsg3vwn0GTQtxbStkIPgsQE$> ________________________________ To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1 ________________________________ To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1 ________________________________ To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1 ######################################################################## To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1
