The cotton bollworm H. armigera, which feeds on important crops e.g. Cotton, Tomatoes,
Corn, Soyebeans etc, is causing detrimental damage every year worldwide, negatively
affecting the agricultural economic production. The need is to look for more
pronounced and effective insecticides. Cholesterol is the intermediate precursor
of steroid hormones in insects and plays a pivotal role in their embryology and
reproduction. Sterol carrier gene (SCP-2) possesses cholesterol binding sites
and is responsible for cholesterol uptake, transfer and accumulation during insect’s
ontogeny. The present study was conducted to evaluate the structure and
function of SCP-2 protein as a potential target to develop novel insecticides
against H. armigera.  In order to address the research questions, recombinant
protein was made by the
construction of HaSCP-2 recombinant plasmid. Protein was purified and its
structure and function was elucidated by NMR spectroscopy. Then Interaction
of HaSCP-2 with lipid and sterol molecules was carried out by the docking
simulation which indicated that lipid such as cholesterol, ?
–sitosterol and palmitic acid could bind to HaSCP-2 with
high docking scores, suggested that HaSCP-2 may interact with cholesterol or
fatty acids through these important sites. Furthermore, NBD-cholesterol binding assays were
performed to investigate ligand binding activity of HaSCP-2. It demonstrated
that HaSCP-2 may play an important role in the cholesterol absorption and
transportation in the cotton bollworm.
It was further confirmed by mutagenesis experiments which indicated Y51,
F53, F89, F110, I117 and Q131 may be the key functional sites involved
in the intracellular hydrophobic interaction between HaSCP-2 and cholesterol
which serves as a sieve for the transportation of sterol. High cholesterol
binding activity was shown by HaSCP-2 and SCP-2 inhibitors (SCPIs) could have
the potential to inhibit the biological activity of HaSCP-2. In vivo Biological
assays reveled that SCPI-treated larvae at young stage showed a significant
decrease of cholesterol uptake. This novel study  thus represent an outstanding effort to
elucidate the NMR structure of SCP-2 in H. armigera and revealed its
important function in cholesterol uptake which paved the
way for designing of potent environmentally
friendly pesticides exploiting  SCP-2
with greater efficacy.

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