Timing alters how a heat shock affects a host-parasitoid interaction

Abiotic factors' effects on species are now well-studied, yet they are still often difficult to predict, especially for strongly interacting species. If these altered abiotic factors and species interactions occur as discrete events in time, such complications may occur because of the events’ relative timing. One such discrete abiotic factor is the short-duration, large magnitude increase in temperature called a heat shock. This study investigates how the timing of heat shocks affects the successful attack and reproduction of a parasitoid wasp (Aphidius ervi) attacking its host, the pea aphid (Acyrthosiphon pisum). We tested three relative timings: 1) heat shock before the wasp attacks hosts, 2) heat shock while the wasp is foraging, and 3) heat shock after the wasp has attacked hosts. In each scenario we compared wasp mummy production (pupal stage) with and without a heat shock. Our results showed that a heat shock had the largest effect when it occurred while wasps actively foraged, with fewer mummies produced when exposed to a heat shock compared to the no heat shock control. Follow-up behavioral tests suggest this was caused by wasps becoming inactive during heat shocks. In contrast, when heat shocks were applied three days before or after foraging, we found no difference in mummy production between the heat shock treatment and no heat shock control. These results show the potential importance of timing when considering the ramifications of an altered abiotic factor, especially with relatively discrete abiotic events and interactions.     

Advances on Vibrio parahaemolyticus research in the postgenomic era

Vibrio parahaemolyticus is a leading cause of seafood-borne bacterial gastroenteritis in humans. Since its discovery in 1950, this bacterium has been isolated in widespread outbreaks and in sporadic cases of gastroenteritis worldwide. Although the exotoxin, thermostable direct hemolysin, had been the focus of extensive research on the pathogenicity of V. parahaemolyticus, the whole-genome sequencing of a clinical isolate, RIMD2210633 strain, was a breakthrough in this field. The possession of two sets of gene clusters for type III secretion systems (T3SS1 and T3SS2) was unveiled by that genome project. T3SS is a protein export apparatus that delivers bacterial proteins, called effectors, directly into the host's cytosol, to disrupt host cell function. The subsequent studies have established that T3SS2, which is encoded in an 80 kb pathogenicity island called V. parahaemolyticus pathogenicity island (Vp-PAI), is closely related to enteropathogenicity. Recent functional analyses of Vp-PAI-encoded genes revealed the sophisticated mechanisms in V. parahaemolyticus for sensing the intestinal environment and host cell contact, and a dozen T3SS2-exported proteins encoded in Vp-PAI. In this review, we summarize recent advances in V. parahaemolyticus research regarding the control of the expression of Vp-PAI-encoded genes, structural components and the secretory regulation of T3SS2, and the biological activities of T3SS2-exported effectors. Thus, Vp-PAI-encoded T3SS2 becomes an important key in the postgenomic era to shed light on the enteropathogenic mechanism of V. parahaemolyticus.     

Cover Image,Volume 88, Issue 6

Hsp16.3, a molecular chaperone, plays a vital role in the growth and survival of Mycobacterium tuberculosis inside the host. We previously reported that deletion of three amino acid residues (¹⁴²STN¹⁴⁴) from C-terminal extension (CTE) of Hsp16.3 triggers its structural perturbation and increases its chaperone activity, which reaches its apex upon the deletion of its entire CTE (¹⁴¹RSTN¹⁴⁴). Thus, we hypothesized that Arg141 (R141) and Ser142 (S142) in the CTE of Hsp16.3 possibly hold the key in maintaining its native-like structure and chaperone activity. To test this hypothesis, we generated two deletion mutants in which R141 and S142 were deleted individually (Hsp16.3ΔR141 and Hsp16.3ΔS142) and three substitution mutants in which R141 was replaced by lysine (Hsp16.3R141K), alanine (Hsp16.3R141A), and glutamic acid (Hsp16.3R141E), respectively. Hsp16.3ΔS142 or Hsp16.3R141K mutant has native-like structure and chaperone activity. Deletion of R141 from the CTE (Hsp16.3ΔR141) perturbs the secondary and tertiary structure, lowers the subunit exchange dynamics and decreases the chaperone activity of Hsp16.3. But, the substitution of R141 with alanine (Hsp16.3R141A) or glutamic acid (Hsp16.3R141E) perturbs its secondary and tertiary structure. Surprisingly, such charge tampering of R141 enhances the subunit exchange dynamics and chaperone activity of Hsp16.3. Interestingly, neither the deletion of R141/S142 nor the substitution of R141 with lysine, alanine and glutamic acid affects the oligomeric mass/size of Hsp16.3. Overall, our study suggests that R141 (especially the positive charge on R141) plays a crucial role in maintaining the native-like structure as well as in regulating subunit exchange dynamics and chaperone activity of Hsp16.3.     

Anisotropic intersubunit and inter-ring interactions revealed in the native bullet-shaped chaperonin complex from Thermus thermophilus

Background

The recent morphological studies on chaperonins have revealed that nearly equivalent amount of symmetric GroEL–(GroES)₂ (football-shaped) and asymmetric GroEL–GroES (bullet-shaped) complexes coexist during the chaperonin reaction cycle, which prompted us to reexamine the equatorial split observed for chaperonin from Thermus thermophilus by implementing semi-empirical molecular orbital (MO) calculations, since it is now believed that the symmetric formation is a precursor to the equatorial split.

Methods

Semi-empirical MO calculations were employed to investigate the intersubunit interactions within the bullet-shaped T. thermophilus chaperonin capturing the substrate of folding intermediates. Interaction energies between each cis-GroEL subunit and closely related remaining subunits in cis-GroEL ring, or in trans-GroEL ring across the equatorial plane, and further, interaction energies between each GroES subunit and adjacent subunits in the same GroES ring and in cis-GroEL ring were simulated.

Results

Anisotropic intensities and energy distribution of the subunits were revealed by the calculations, which are consistent with two conformations of the subunits forming cis-GroEL ring as revealed by X-ray crystal structure, and with an anisotropic critical binding site on cis-GroEL ring for chaperonin functioning.

Conclusions

This is the first application of semi-empirical MO calculations to the macromolecular complex of the native bullet-shaped chaperonin (GroEL–GroES–ADP homolog) from T. thermophilus.

General significance

The results also appear to support the occurrence of the equatorial split for T. thermophilus chaperonin observed via electron microscopy, but has not yet been fully observed for Escherichia coli GroEL–GroES system.     

Extremity cooling for heat stress mitigation in military and occupational settings

Physical work, high ambient temperature and wearing protective clothing can elevate body temperature and cardiovascular strain sufficiently to degrade performance and induce heat-related illnesses. We have recently developed an Arm Immersion Cooling System (AICS) for use in military training environments and this paper will review literature supporting such an approach and provide details regarding its construction. Extremity cooling in cool or cold water can accelerate body (core temperature) cooling from 0.2 to 1.0 °C/10 min vs. control conditions, depending on the size/surface area of the extremity immersed. Arm immersion up to the elbow results in greater heat loss than hand- or foot-only immersion and may reduce cardiovascular strain by lowering heart rate by 10–25 beats/min and increase work tolerance time by up to 60%. The findings from studies in this paper support the use of AICS prototypes, which have been incorporated as part of the heat stress mitigation procedures employed in US Army Ranger Training and may have great application for sports and occupational use.     

The polymorphism in the promoter region of metallothionein 1 is associated with heat tolerance of scallop Argopecten irradians

Metallothioneins (MTs), a superfamily of cysteine-rich proteins, perform multiple functions, such as maintaining homeostasis of essential metals, detoxification of toxic metals and scavenging of oxyradicals. In this study, the promoter region of a metallothionein (MT) gene from Bay scallop Argopecten irradians (designed as AiMT1) was cloned by the technique of genomic DNA walking, and the polymorphisms in this region were screened to find their association with susceptibility or tolerance to high temperature stress. One insert–deletion (ins–del) polymorphism and sixteen single nucleotide polymorphisms (SNPs) were identified in the amplified promoter region. Two SNPs, − 375 T–C and − 337 A–C, were selected to analyze their distribution in the two Bay scallop populations collected from southern and northern China coast, which were identified as heat resistant and heat susceptible stocks, respectively. There were three genotypes, T/T, T/C and C/C, at locus − 375, and their frequencies were 25%, 61.1% and 13.9% in the heat susceptible stock, while 34.2%, 42.1% and 23.7% in the resistant stock, respectively. There was no significant difference in the frequency distribution of different genotypes between the two stocks (P > 0.05). In contrast, at locus − 337, three genotypes A/A, A/C and C/C were revealed with the frequencies of 11.6%, 34.9% and 53.5% in the heat susceptible stock, while 45.7%, 32.6% and 21.7% in the heat resistant stock, respectively. The frequency of C/C genotype in the heat susceptible stock was significantly higher (P < 0.01) than that in the heat resistant stock, while the frequency of A/A in the heat resistant stock was significantly higher (P < 0.01) than that in the heat susceptible stock. Furthermore, the expression of AiMT1 mRNA in scallops with C/C genotype was significantly higher than that with A/A genotype (P < 0.05) after an acute heat treatment at 28 °C for 120 min. These results implied that the polymorphism at locus − 337 of AiMT1 was associated with the susceptibility/tolerance of scallops to heat stress, and the − 337 A/A genotype could be a potential marker available in future selection of Bay scallop with heat tolerance.