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Off the top of my head, assuming nothing much about your protein(s) - some of this is only going to work if you can modify the protein(s) prior to crystallization. This excludes the 'normal' heavy atom soaking type stuff which can give rise to binding with covalent-like strength (while still being noncovalent, technically): Iodination of tyrosines (and histidines if pH is selected correctly) Iodination or bromination of DNA/RNA if your complex contains nucleic acid Introduction of heavy atom into a custom-made peptide (sky is the limit as to what you can do with this) followed by peptide ligation (i.e. sortase and the like) - requires modification and re-expression of your protein construct of course Reaction of Lys and N-term with suitably modified carboxylic acids (e.g. para-iodo benzoic acid, para-mercuric derivatives and so on) via the use of water soluble coupling agents or pre-activated acid derivatives Reductive amination of Lys residues using aldehydes that bear heavy atom labels (must be sure that the reducing agent does not knock the HA off, which it jolly well can do) Ditto with side chains of Asp and Glu, and the amine is modified with heavy atom(s) Introduction of unnatural amino acids (even bearing heavy atoms if desired) by means of genetic manipulation (stop codon bypass, codon replacement etc.) Nucleophilic attack on Serine (especially facile if you happen to have a serine protease or something similar where serine is activated) Also see: https://www.nature.com/articles/ncomms5740 Even though these methods are not necessarily selective with respect to amino acids being modified, it is surprisingly often possible to only modify a few (sometimes even one) specific positions in a protein due to the selectivity imposed by protein surface environment I am probably missing another 10-15 methods but gotta run :) Artem - Cosmic Cats approve of this message On Wed, Jan 2, 2019 at 2:42 PM Chandramohan Kattamuri < [log in to unmask]> wrote: > > Dear CCP4 members, Can someone suggest to me a methodology to covalently > modify (non-cysteine) on component of a multicomponent complex with heavy > atoms in order to achieve better phase determination? > > Thanks in advance > > > Chandra > [log in to unmask] > > > > > ------------------------------ > > 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