Abstract:

In this study the safety of the maize and papaya cystatins used to control nematodes and
banana weevil borer was assessed by determining the allergenicity and toxicity of the
proteins using both in vitro as well as the in vivo method of oral gavage using albino rats.
The maize and papaya cystatins were expressed in Esherechia coli strain Ml5 since this
organism is easily cultured. Determination of in vitro digestive assays for both cystatins
as well oral feeding of the animals with the cystatins in xarious concentrations of lOmg,
lOOmg and lOOOmg/kg body weight was carried out followed by sacrificing the animals
on the fourteenth day for clinical and histopathological examination of the blood and
animal organs.

The results indicate that the maize and papaya cystatins were fully expressed in the E.coli
Ml5 and E.coli Ml5 culture grew well to produce enough protein. The two proteins
rapidly degraded in the simulated gastric fluid taking less than 2 minutes to degrade in
the pepsin. The maize and papaya cystatins had amino acid sequence similarity with
Actinidici cleliciosa a kiwi fruit of 48.3% and 40.4% respectively over their full length,
suggesting that both cystatins are not potential allergens. The results of the amino acid
sequence homology comparison with the known toxins in the database did not indicate
any relatives, suggesting that these cystatins are not potential toxins. The feed intake data
showed that the maize and papaya cystatins did not affect feed intake of the animals. The
results of urinalysis, haematology, serum chemistry and organ weights showed that
feeding the rats with acute doses of maize and papaya cystatins did not affect the liver
and kidneys which play a big role in various metabolic processes. This study shows that
the maize and papaya cystatins used to control pests in transgenic bananas in Uganda do
not have allergenic and toxic effects. These cystatins may therefore be safely used in
transgenic bananas to control nematodes and weevils.