Hi Paul, While crystal contacts are typically of a non-covalent nature, there are some exceptions. A disulfide bond can act as a crystal contact, which is a covalent interaction. A technique called synthetic symmetrization involves the engineering of single cysteine mutants, followed by oxidation to form an intermolecular disulfide bond that lies on a 2-fold symmetry axis between the two monomers. The original goal of this technique was to turn an asymmetric monomer into a symmetric dimer, which should crystallize more readily if the artificial 2-fold lies on a crystallographic symmetry axis. Recently, a paper illustrated that even if the artificial 2-fold axis does not become a crystallographic axis, the introduction of a disulfide can create artificial "crystal contacts," which also aid in crystallization. Check out the following paper. There is a nice figure that shows two protein molecules that are really not touching with the exception of the engineered disulfide bond that forms the only contact.
Protein Sci. 2011 Jan;20(1):168-78. Synthetic symmetrization in the crystallization and structure determination of CelA from Thermotoga maritima. HTH, Mike ----- Original Message ----- From: "Paul Lindblom" <[email protected]> To: [email protected] Sent: Wednesday, June 29, 2011 2:22:26 PM GMT -08:00 US/Canada Pacific Subject: [ccp4bb] The Good and the Bad crystal contact? Hi everybody, can anybody tell me how crystal contacts are defined? Are there good and bad crystal contacts? They are the most important interactions with impact on the crystal quality, but they are not of covalent nature, aren´t they? With best regards, Paul -- Michael C. Thompson Graduate Student Biochemistry & Molecular Biology Division Department of Chemistry & Biochemistry University of California, Los Angeles [email protected]
