The chemosensory appendage proteome of Amblyomma americanum (Acari: Ixodidae) reveals putative odorant‐binding and other chemoreception‐related proteins

Abstract

Proteomic analyses were done on 2 chemosensory appendages of the lone star tick, Amblyomma americanum. Proteins in the fore tarsi, which contain the olfactory Haller's organ, and in the palps, that include gustatory sensilla, were compared with proteins in the third tarsi. Also, male and female ticks were compared. Proteins were identified by sequence similarity to known proteins, and by 3-dimensional homology modeling. Proteomic data were also compared with organ-specific transcriptomes from the tick Rhipicephalus microplus. The fore tarsi express a lipocalin not found in the third tarsi or palps. The fore tarsi and palps abundantly express 2 proteins, which are similar to insect odorant-binding proteins (OBPs). Compared with insect OBPs, the tick OBP-like sequences lacked the cysteine absent in C-minus OBPs, and 1 tick OBP-like sequence had additional cysteines that were similar to C-plus OBPs. Four proteins similar to the antibiotic protein microplusin were found: 2 exclusively expressed in the fore tarsi and 1 exclusively expressed in the palps. These proteins lack the microplusin copper-binding site, but they are modeled to have a significant internal cavity, potentially a ligand-binding site. Proteins similar to the dust mite allergens Der p7 and Der f 7 were found differentially expressed in female fore tarsi. A protein exclusively expressed in the fore tarsi has similarities to Neto, which is known to be involved in clustering of ionotropic glutamate receptors. These results constitute the first report of OBP-like protein sequences in ticks and point to several research avenues on tick chemosensory reception.

Varroa chemosensory proteins: some are conserved across Arthropoda but others are arachnid specific

“…The other two Varroa OBPs lacked the conserved domain, but significantly matched 'OBP-like' sequences identified in I. scapularis, G. occidentalis and A. americanum and reported by Renthal et al, (2017) (BLASTn, e-value < 1E-20). Four of the six Varroa OBPs were identified according to the presence of the insect OBP conserved domain (IPR036728).…”

“…of the 'OBP-like' proteins reported by Renthal et al, (2017), and found four Varroa transcripts (local BLAST, e-value < E-20), two of which also classified as 'OBP' containing the insect-OBP domain in addition to a signal peptide in the N-terminal of the open reading frame (ORF). of the 'OBP-like' proteins reported by Renthal et al, (2017), and found four Varroa transcripts (local BLAST, e-value < E-20), two of which also classified as 'OBP' containing the insect-OBP domain in addition to a signal peptide in the N-terminal of the open reading frame (ORF).…”

“…The tree was constructed using PhyMl (Guindon et al, 2010) under the WAG (Whelan and Goldman, 2001) + Gamma rates (G) + Invariant sites (I) models of substitution selected by PhyMl-SMS (Lef or t et al, 2017), and is based on the amino acid alignment using Mafft (Katoh and Standley, 2013). The original names of I. scapularis sequences Ix2 and Ix3 are OBPL2 and OBPL1, respectively, were used, according to Renthal et al, (2017) and Josek et al, (2018). Leaves are coloured according to the organisms' classes: Arachnida (red), Insecta (blue) and Collembola (green).…”

“…CSPs have been found in most of the arthropods investigated to date (Eyun et al, 2017). Gulia-Nuss et al, 2016) whereas the presence of CSPs in A. americanum is inconsistent; no CSPs were found by Renthal et al, (2017) but one copy was detected by Vieira and Rozas (2011). In arachnids, one CSP gene was found in I. scapularis (Vieira and Rozas, 2011; (Katoh and Standley, 2013).…”

“…For example, the 'OBP-like' proteins were described by Renthal et al, (2017) as a subgroup of the known insect OBPs but lacking the classic insect OBP domain. It seems that a domain-based classification is elusive as the presence of the conserved domain heavily depends on the sequence credibility, the search algorithm and its threshold, and the constantly changing databases.…”