GAPES4 (GAmmaproteobacterial PEriplasmic Sensor) domain is a periplasmic sensor domain found in various GGDEF- and EAL-containing proteins. In Escherichia coli, GAPES4 forms the N-terminal domain of the regulatory protein CsrD (YhdA) [1], which contains enzymatically inactive GGDEF and EAL domains and controls CsrD) that controls the degradation of two non-coding RNAs, CsrB and CsrC [2,3]. In Vibrio cholerae, GAPES4-containing protein MshH (Q9KUW1_VIBCH) inhibits biofilm formation, apparently acting through the glucose-specific enzyme IIA (Q9KTD8, Pfam:PF00358) [4].

1: Systematic Nomenclature for GGDEF and EAL Domain-Containing Cyclic Di-GMP Turnover Proteins of Escherichia coli. Hengge R, Galperin MY, Ghigo JM, Gomelsky M, Green J, Hughes KT, Jenal U, Landini P; J Bacteriol. 2015;198:7-11. PMID:26148715

2: Identification of a novel regulatory protein (CsrD) that targets the global regulatory RNAs CsrB and CsrC for degradation by RNase E. Suzuki K, Babitzke P, Kushner SR, Romeo T; Genes Dev. 2006;20:2605-2617. PMID:16980588

3: Post-transcriptional regulation on a global scale: form and function of Csr/Rsm systems. Romeo T, Vakulskas CA, Babitzke P; Environ Microbiol. 2013;15:313-324. PMID:22672726

4: Glucose-specific enzyme IIA has unique binding partners in the vibrio cholerae biofilm. Pickering BS, Smith DR, Watnick PI; MBio. 2012;3:e00228-e00212. PMID:23131828