Walrycin B is an inhibitor of WalR [1].

Walrycin B is screened out from a chemical library. It is proved to be a selective WalR inhibitor by measuring EGFP fluorescence intensity. In this assay, it is found to strongly increase fluorescence intensity in strain JM109/pFI014 but has no significant effect on the strain JM109/pFI001. Walrycin B shows effects on the expression of WalR regulon genes in the in vivo assay. The addition of it lowers the expression of ydjM, yocH and yvcE and increases the expression of yoeB and yjeA rapidly. These effects caused by Walrycin B are opposite with which caused by WalR suggesting that Walrycin B specifically affects the WalK/WalR system. Since WalK/WalR plays a regulating role in cell wall metabolism and cell division in Bacillus subtilis and Staphylococcus aureus, Walrycin B is found to cause cell death in both of them with strong MICs through targeting WalR [1].

References:
[1] Gotoh Y, Doi A, Furuta E, Dubrac S, Ishizaki Y, Okada M, Igarashi M, Misawa N, Yoshikawa H, Okajima T, Msadek T, Utsumi R. Novel antibacterial compounds specifically targeting the essential WalR response regulator. J Antibiot (Tokyo). 2010 Mar;63(3):127-34.