Response of leucine-rich repeat domain-containing protein in Haemaphysalis longicornis to Babesia microti infection and its ligand identification

Haemaphysalis longicornis is a blood-feeding hard tick known for transmitting a variety of pathogens, including Babesia. How the parasites in the imbibed blood become anchored in the midgut of ticks is still unknown. Leucine-rich repeat domain (LRR)-containing protein, which is associated with the innate immune reaction and conserved in many species, has been detected in H. longicornis and has previously been indicated in inhibiting the growth of Babesia gibsoni. However, the detailed mechanism is unknown. In this study, one of the ligands for LRR from H. longicornis (HlLRR) was identified in B. microti, designated as BmActin (Babesia microti actin), using GST pull-down experiments and immunofluorescence assay. Moreover, RNA interference of HlLRR led to a decrease in the BmActin mRNA expression in the midgut of fully engorged ticks, which fed on B. microti-infected mice. We also found that the expression level of the innate immune molecules in H. longicornis, defensin, antimicrobial peptides (AMPs), and lysozyme were downregulated after the knockdown of HlLRR. However, subolesin expression was upregulated. These results indicate that HlLRR not only recognizes BmActin but may also modulate innate immunity in ticks to influence Babesia growth, which will further benefit the development of anti-Babesia vaccines or drugs.

Novel Gene Deletion in NLRC4 Expanding the Familial Cold Inflammatory Syndrome Phenotype

Familial cold inflammatory syndrome (FCAS) is a rare, inherited inflammatory disease characterized by episodes of fever, rash, and arthralgias after exposure to cold stimuli. Previous literature has established FCAS linked to autosomal dominant mutations in the NLRP3 (CIAS1) and NLRP12 genes. Moreover, there has been recent evidence of NLRC4-inflammasomopathies. Although there have been cases of FCAS secondary to missense mutations in NLRC4, we report the first symptomatic case associated with a 93-base-pair in-frame deletion within Exon 5 of the leucine rich repeat domain.

Crystal structure of a ligand-free stable TSH receptor leucine-rich repeat domain

The crystal structures of the thyroid-stimulating hormone receptor (TSHR) leucine-rich repeat domain (amino acids 22–260; TSHR260) in complex with a stimulating human monoclonal autoantibody (M22TM) and in complex with a blocking human autoantibody (K1-70™) have been solved. However, attempts to purify and crystallise free TSHR260, that is not bound to an autoantibody, have been unsuccessful due to the poor stability of free TSHR260. We now describe a TSHR260 mutant that has been stabilised by the introduction of six mutations (H63C, R112P, D143P, D151E, V169R and I253R) to form TSHR260-JMG55TM, which is approximately 900 times more thermostable than wild-type TSHR260. These six mutations did not affect the binding of human TSHR monoclonal autoantibodies or patient serum TSHR autoantibodies to the TSHR260. Furthermore, the response of full-length TSHR to stimulation by TSH or human TSHR monoclonal autoantibodies was not affected by the six mutations. Thermostable TSHR260-JMG55TM has been purified and crystallised without ligand and the structure solved at 2.83 Å resolution. This is the first reported structure of a glycoprotein hormone receptor crystallised without ligand. The unbound TSHR260-JMG55TM structure and the M22 and K1-70 bound TSHR260 structures are remarkably similar except for small changes in side chain conformations. This suggests that neither the mutations nor the binding of M22TM or K1-70TM change the rigid leucine-rich repeat domain structure of TSHR260. The solved TSHR260-JMG55TM structure provides a rationale as to why the six mutations have a thermostabilising effect and provides helpful guidelines for thermostabilisation strategies of other soluble protein domains.