4WKM:
reference: The beta-lactamase Gene Regulator AmpR is a Tetramer that Recognizes and Binds the D-Ala-D-Ala Motif of its Repressor UDP-MurNAc-pentapeptide., Vadlamani G, Thomas MD, Patel TR, Donald LJ, Reeve TM, Stetefeld J, Standing KG, Vocadlo DJ, Mark BL, J Biol Chem. 2014 Dec 5. pii: jbc.M114.618199. PMID: 25480792

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