Hi All

To prevent Phenix removing link records, you can use Readyset to create a 
parameters file based on LINK records, and feed it to the refinement program, 
otherwhise they are deleted.

Best wishes

Matthew.
________________________________
From: CCP4 bulletin board <CCP4BB@JISCMAIL.AC.UK> on behalf of Nicholas Clark 
<ndcla...@buffalo.edu>
Sent: 14 August 2022 16:01
To: CCP4BB@JISCMAIL.AC.UK <CCP4BB@JISCMAIL.AC.UK>
Subject: Re: [ccp4bb] circular peptide structure refinement

Phenix in the past, and I’m assuming still, does not recognize “link records”. 
You’ll likely need to generate the peptide in AceDRG, making sure to link the 
carboxy- and amino-termini, and include the cif during refinement.

This was the only way I was able to get Phenix to properly refine an inhibitor 
covalently linked to an active site Cys. Thus, the same procedure may be 
required for your circular peptide.

Best,

Nick Clark

On Sun, Aug 14, 2022 at 1:06 AM Jiang Xu 
<foxj...@gmail.com<mailto:foxj...@gmail.com>> wrote:
Hi Joel,
     Thank you for your reply. I just got time to refine the circular peptide 
structure 1 month later. I use MR to solve the structure. I made the 
link(Calculate-->Modeling-->Make Link) as the guy who replied to my question 
suggested. The link generated is a dashed line but disappeared after refinement 
with Phenix.  It seemed that the program didn't consider the link made in coot 
as a valid bond and intentionally avoided forming a bond between the C atom and 
the N atom. I still don't know how to fix the problem.
Thank you,
Best regards,
Jiang
Lin Chen Lab
University of Southern California

P.S.
coot manually made link between the C and N terminal
[unnamed.jpg]
After refinement
[unnamed (1).jpg]



On Wed, Jul 6, 2022 at 3:29 PM Joel Tyndall 
<joel.tynd...@otago.ac.nz<mailto:joel.tynd...@otago.ac.nz>> wrote:

You will need to add the “link” line to the PDB file so the software recognises 
the covalent bond.

See the pdb file for 6U6K



Hope this helps



J



From: CCP4 bulletin board <CCP4BB@JISCMAIL.AC.UK<mailto:CCP4BB@JISCMAIL.AC.UK>> 
On Behalf Of Jiang Xu
Sent: Thursday, 7 July 2022 10:15 AM
To: CCP4BB@JISCMAIL.AC.UK<mailto:CCP4BB@JISCMAIL.AC.UK>
Subject: [ccp4bb] circular peptide structure refinement



Hello everyone,

   I have a peptide that forms a peptide bond between the N terminal and C 
terminal.  I used X-ray crystallography to solve the structure and found the N 
and C terminals are pretty close to each other with extra electron densities 
clearly showing that they form a peptide bond. However in Coot I could not make 
the peptide bond, the two terminals seem to repel each other when I do real 
space refinement in coot and, couldn't form the peptide bond. Any suggestions 
on how to do it?

Thank you,

Best,

Jiang Xu

Lin Chen Research Group

Molecular and Computational Biology

Department of Biological Sciences

University of Southern California



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--
Nicholas D. Clark
PhD Candidate
Malkowski Lab
University at Buffalo
Department of Structural Biology
Jacob's School of Medicine & Biomedical Sciences
955 Main Street, RM 5130
Buffalo, NY 14203

Cell: 716-830-1908

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