Abstract
BackgroundHeat resistance is a common characteristic of harpins, a class of proteins found in Gram-negative bacteria, which may be related to the stability of coiled-coil (CC) structure. The CC structure is a ubiquitous protein folding and assembly motif made of α-helices wrapping around each other forming a supercoil. Specifically, whether the stability of the CC structure near to N-terminus of four selected harpin proteins from Xanthomonas (hereafter referred to as Hpa1) would influence their characteristics of heat resistance was investigated. We used bioinformatics approach to predict the structure of Hpa1, used the performance of hypersensitive response (HR)-induction activity of Hpa1 and circular dichroism (CD) spectral analyses to detect the relationship between the stability of the CC structure of Hpa1 and heat resistance.ResultsEach of four-selected Hpa1 has two α-helical regions with one in their N-terminus that could form CC structure, and the other in their C-terminus that could not. And the important amino acid residues involved in the CC motifs are located on helices present on the surface of these proteins, indicating they may engage in the formation of oligo mericaggregates, which may be responsible for HR elicitation by harpins and their high thermal stability. Increased or decreased the probability of forming a CC could either induce a stronger HR response or eliminate the ability to induce HR in tobacco after high temperature treatment. In addition, although the four Hpa1 mutants had little effect on the induction of HR by Hpa1, its thermal stability was significantly decreased. The α-helical content increased with increasing temperature, and the secondary structures of Hpa1 became almost entirely α-helices when the temperature reached 200 °C. Moreover, the stability of the CC structure near to N-terminus was found to be positively correlated with the heat resistance of Hpa1.ConclusionsThe stability of the CC structure might sever as an inner drive for mediating the heat resistance of harpin proteins. Our results offer a new insight into the interpretation of the mechanism involved in the heat resistance of harpin protein and provide a theoretical basis for further harpin function investigations and structure modifications.
Highlights
Heat resistance is a common characteristic of harpins, a class of proteins found in Gram-negative bacteria, which may be related to the stability of coiled-coil (CC) structure
Another one is that a coiled-coil (CC) structure forming at N-terminal α-helical region in HpaXcm from X. citri pv. mangiferaeindicae [2] might attribute to the thermal stability of Hapin
Consistent with the results obtained from the secondary structure, each protein is composed predominantly of two major helical regions (i.e., HpaXm stretch-1 residues 36–52, stretch-2 residues 84–101; Hpa1Xoo stretch-1 residues 37–53, stretch-2 residues 87–101; HpaXpm stretch-1 residues 41–57, HpaXpm stretch-2 residues 93–109; HpaXcm stretch-1 residues 37–53, stretch-2 residues 89– 106) connected by turns and loops (Fig. 1b)
Summary
Heat resistance is a common characteristic of harpins, a class of proteins found in Gram-negative bacteria, which may be related to the stability of coiled-coil (CC) structure. We used bioinformatics approach to predict the structure of Hpa, used the performance of hypersensitive response (HR)induction activity of Hpa and circular dichroism (CD) spectral analyses to detect the relationship between the stability of the CC structure of Hpa and heat resistance. Proteins could lose their functional activities under various stress conditions, mainly due to the destruction of their active three-dimensional (3-D) structure [1]. The factors affect the heat resistance of harpin protein is still unclear
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