Cystine knot toxins (CKTs) in spider venoms represent a rich source of novel ligands for varied ion channels. Here, we identified 95 novel putative CKT precursors by analyzing expressed sequence tags of the tarantula Chilobrachys jingzhao venom gland. Phylogenetics analyses revealed one orphan family and six families with sequence similarity to known toxins. To further investigate the relationships of their structures, functions and evolution, we assayed 10 representative toxins for their effect on ion channels, and performed structure model comparisons, evolution analysis and toxin distribution analysis. This study revealed two major types of CKTs: pore-blocking toxins and gating modifier toxins. A few blockers were observed with relatively high abundance and wide distribution, which may be a category of original toxins that block channels conserved in various preys with relatively high specificity. The gating modifier families contain advanced toxins, usually have many members and interact with diverse regulatory components of channels.
Venomous animals possess an arsenal of toxins for predation and defense. These toxins have great diversity in function and structure as well as evolution and therefore are of value in both basic and applied research. Recently, toxinomics researches using cDNA library sequencing and proteomics profiling have revealed a large number of new toxins. Although several previous groups have attempted to manage these data, most of them are restricted to certain taxonomic groups and/or lack effective systems for data query and access. In addition, the description of the function and the classification of toxins is rather inconsistent resulting in a barrier against exchanging and comparing the data. Here, we report the ATDB database and website which contains more than 3235 animal toxins from UniProtKB/Swiss-Prot and TrEMBL and related toxin databases as well as published literature. A new ontology (Toxin Ontology) was constructed to standardize the toxin annotations, which includes 745 distinct terms within four term spaces. Furthermore, more than 8423 TO terms have been manually assigned to 2132 toxins by trained biologists. Queries to the database can be conducted via a user-friendly web interface at http://protchem.hunnu.edu.cn/toxin.
The coding sequence of huwentoxin-I, a neurotoxic peptide isolated from the venom of the Chinese spider Ornithoctonus huwena, was amplified by PCR using the cDNA library constructed from the spider venom glands. The cloned fragment was inserted into the expression vector pET-40b and transformed into the E. coli strain BL21 (DE3). The expression of a soluble fusion protein, disulfide interchange protein (DsbC)-huwentoxin-I, was auto-induced in the periplasm of E. coli in the absence of IPTG. After partial purification using a Ni-NTA column, the expressed fusion protein was digested using enterokinase to release heteroexpressed huwentoxin-I and was further purified using RP-HPLC. The resulting peptide was subjected to gel electrophoresis and mass spectrometry analysis. The molecular weight of the heteroexpressed huwentoxin-I was 3750.69, which is identical to that of the natural form of the peptide isolated from spider venom. The physiological properties of the heteroexpressed huwentoxin-I were further analyzed using a whole-cell patch clamp assay. The heteroexpressed huwentoxin-I was able to block currents generated by human Nav1.7 at an IC50 of 640 nmole/L, similar to that of the natural huwentoxin-I, which is 630 nmole/L.
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