As other said, having co-crystal doesn’t mean you will have measurable affinity. Further no heat in ITC experiments doesn’t mean no binding. Which buffer you used during previous ITC experiment? If heat in the previous experiment (wild type) was due to heat of ionization and you removed the residue involved in protonation/deprotonation event, you will not see any heat. If there is 10-20 fold decrease in affinity by mutation, you may not be able to see significant heat during ITC experiment as well.
Dhiraj ________________________________ From: CCP4 bulletin board <CCP4BB@JISCMAIL.AC.UK> on behalf of vipul panchal <vipanch...@gmail.com> Sent: Saturday, February 22, 2020 3:25 AM To: CCP4BB@JISCMAIL.AC.UK <CCP4BB@JISCMAIL.AC.UK> Subject: Re: [ccp4bb] Contradictory result between ITC and cocrystal structure Hi Monika, If the protein cocrystalize with ligand doesn't mean it interacts with protein. You have provided insufficient information here. Does the ligand is bound to mutant protein with atleast 2 or 3 hydrogen bonds (how many residues are mutated?) ? If no that means, it is just cocrystalizing but not interacting with mutant protein. Another possibility is, during cocrystalization ligand concentration is very high so as to force the interaction which otherwise is not possible as you observed with ITC. In other terms, affinity is too low to be detected by ITC. Cheers, Vipul On Sat, 22 Feb, 2020, 12:01 PM monika chandravanshi, <chandravanshi.monik...@gmail.com<mailto:chandravanshi.monik...@gmail.com>> wrote: Dear All, I have a situation, where a mutant protein does not exhibit any heat change upon titration with cognate ligand in the ITC experiment. However, it co-crystallizes with the respective cognate ligand. Also, the cocrystal structure reveals the conservation of the hydrogen bonding networks except for the mutated residues. I would like to know the possible reason for the no heat change in the ITC experiment. Looking forward to hearing from you. -- ----- With Kind Regards Monika Chandravanshi PhD Scholar, Department of Biosciences and Bioengineering Indian Institute of Technology Guwahati, Guwahati India ________________________________ 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
