The HAMP Linker in Histidine Kinase Dimeric Receptors Is Critical for Symmetric Transmembrane Signal Transduction

Abstract

The HAMP linker, a common structural element between a sensor and a transmitter module in various sensor proteins, plays an essential role in signal transduction. Here, by in vivo complementation experiments with Tar-EnvZ hybrid receptor mutants in which the HAMP linker forms a heterodimer with Tar and EnvZtype subunits, we found that mutations at one linker only affect the function of EnvZ in the same subunit. However, the same mutations affect the EnvZ function of both subunits when only a Tar or EnvZ-type HAMP linker is used. These results suggest that intersubunit interactions in the HAMP linker normally mediate signal transduction through both subunits in a sensor dimer, whereas the signal is asymmetrically transduced through the linker in a heterodimer. This is the first demonstration that two HAMP linkers in a sensor dimer are functionally coupled for normal signal transduction; however, this functional coupling can be reduced when the HAMP linkers lose their symmetric nature.The HAMP linker is widely found in histidine kinases, chemoreceptors, bacterial nucleotidyl cyclases, and phosphatases (1-3). Although the primary sequence homology among predicted HAMP linkers is low, they all share a similar helix-turnhelix fold based on secondary structure prediction. A cysteinescanning study on the Tar linker supports this model of HAMP linker structure (4).Genetic analysis found a number of mutations clustered in the HAMP linker of various sensor proteins, which usually lead to biased signaling modes (5-9). This suggests that the HAMP linker plays an active role in signal transduction rather than being just a simple structural element connecting the sensor and transmitter modules of sensor proteins. However, the exact function of the HAMP linker on signal transduction remains to be determined.Functional hybrid histidine kinases have been constructed by fusing the sensor module of chemoreceptors (also called methyl-accepting chemotaxis proteins) to the transmitter module of histidine kinase EnvZ using the HAMP linker from either protein. In Taz1, the sensor module of chemoreceptor Tar is fused to the transmitter module of EnvZ using the Tar linker (10). In Trz, the sensor module of chemoreceptor Trg is fused to the transmitter module of EnvZ using the Trg linker (11). In Tez1A1 and Tez1PQ, the sensor module of Tar is fused to the transmitter module of EnvZ using the EnvZ linker with one Ala insertion at the N-terminal end and the EnvZ linker with a Pro to Gln mutation at position 185 (the position number is based on EnvZ sequence), respectively (12). A number of functional hybrid histidine kinases have also been constructed by fusing the sensor module of one histidine kinase with the transmitter module of another histidine kinase at the HAMP linker region (NarQ-NarX, NarX-NarQ, and NarX-CpxA fusions) or by replacing the HAMP linker of one histidine kinase (NarX) with the HAMP linker of another histidine kinase (CpxA) (13). In addition, functional hybrid chemoreceptors have been constructed in which Tar-Tsr (14), ...

The influence of acetyl phosphate on DspA signalling in the Cyanobacterium Synechocystis sp. PCC6803

“…The identification of transmembrane sequences by SMART is with an accuracy of 97–98% [23]. Because the 145 amino acid region that is flanked by the two transmembrane regions is highly conserved in all 15 cyanobacterial sequences and Porphyra (see additional figure online and Prodom Family PD339187 [24]) and it is adjacent and upstream of a HAMP domain (which is known to in most cases be actively involved in transmission of signals from a periplasmic signalling domain to the cytoplasmic portion of the protein [12,25,26]), we think it probably functions as a periplasmic sensor. We have not been able to detect homologous sequences in any other protein sequence, suggesting that it is unique to Ycf26 (DspA/NblS).…”

Probing bacterial transmembrane histidine kinase receptor–ligand interactions with natural and synthetic molecules

“…1A). CqsS lacks a HAMP domain, which is important in signal transduction in many histidine kinases (32)(33)(34)(35)(36)(37)(38). Thus, interactions between CAI-1 and the final transmembrane domain suggest that this transmembrane domain serves not only in ligand binding but as a critical regulatory region for CqsS kinase activity.…”

Cyanobacterial Two-Component Proteins: Structure,Diversity, Distribution, andEvolution

“…Kinases of HK class III (HKIII) possess, in addition to the HisKA and HATPase, a HAMP (or "linker") domain. The latter is typically found downstream from the last TM segment of a protein, and it has been shown that two symmetrical HAMP domains dimerize and cooperate to transfer the signal across the membrane via a linker to the histidine kinase (155). The presence of a HAMP domain suggests that the corresponding putative ORFs likely function as a dimer.…”