Region 2.1 of the Escherichia coli heat-shock sigma factor RpoH (σ 32) is necessary but not sufficient for degradation by the FtsH protease

Abstract

The cellular level of the Escherichia coli heat-shock sigma factor RpoH (s 32 ) is negatively controlled by chaperone-mediated proteolysis through the essential metalloprotease FtsH. Point mutations in the highly conserved region 2.1 stabilize RpoH in vivo. To assess the importance of this turnover element, hybrid proteins were constructed between E. coli RpoH and Bradyrhizobium japonicum RpoH 1 , a stable RpoH protein that differs from region 2.1 of E. coli RpoH at several positions. Nine amino acids forming a putative a-helix were exchanged between the two proteins. Both hybrids were active sigma factors and showed intermediate protein stability.

Dual Role of FtsH in Regulating Lipopolysaccharide Biosynthesis in Escherichia coli

“…Thus, in the case of 32 , the highly conserved region 2.1 appears to be essential for in vivo degradation (5,16,28,29). However, this region is not sufficient for degradation.…”

When, how and why? Regulated proteolysis by the essential FtsH protease in Escherichia coli

“…Führer et al, 2006 HflD, HflK/C; C terminus (Kihara et al, 1997(Kihara et al, , 2001Shotland et al, 1997;Kobiler et al, 2002) λCIII Internal; terminal (Herman et al, 1997) λXis ND (Leffers and Gottesman, 1998) RpoH DnaK/J, GroEL/ES; internal (Herman et al, 1995;Horikoshi et al, 2004;Obrist and Narberhaus, 2005;Obrist et al, 2007Obrist et al, , 2009 Gottesman, 1998; Kobiler et al, 2002) and various stress responses. For most of these FtsH substrates, the mechanistic details of recognition and degradation are not yet understood.…”

“…This internal and structured degron does not seem to be sufficient for FtsH-dependent degradation of RpoH as point mutations in this region did not stabilize RpoH completely. Moreover, introduction of RpoH-region 2.1 into the sigma factor RpoS, a ClpXP substrate, did not convert RpoS into an FtsH substrate (Obrist et al, 2007). A second turnover element for FtsH-dependent RpoH degradation lies in region C, a region located in the center of the sigma factor (Obrist et al, 2009), which is needed for binding of the RNAP (Nakahigashi et al, 1995;Joo et al, 1998;Arsène et al, 1999 Figure 2C).…”

“…Combination of amino acid exchanges in region 2.1 and region C drastically stabilized RpoH. Most importantly, an RpoH fragment (residues 37-147) comprised of region 2.1 and region C is degraded by FtsH suggesting that these two regions are sufficient for specific recognition (Obrist and Narberhaus, 2005;Obrist et al, 2007Obrist et al, , 2009. DnaJ interacts directly with region 2.1 (Rodriguez et al, 2008;Suzuki et al, 2012;Noguchi et al, 2014;Miyazaki et al, 2016) and it is assumed that DnaJ-induced conformational changes promote DnaK-binding to region 3.2 of RpoH (Rodriguez et al, 2008).…”

Conditional Proteolysis of the Membrane Protein YfgM by the FtsH Protease Depends on a Novel N-terminal Degron

“…Degradation of the heat shock sigma factor RpoH ( 32 ) involves the chaperones DnaK, DnaJ, and GroEL (11,13,18,22). The RpoH degron is a structured motif located in an exposed ␣ helix (15,23). Because of its localization in the inner membrane, FtsH is predestined to degrade membrane proteins such as YccA, SecY, PspC, and F 0 a.…”