In silico analyses of structural and allergenicity features of sapodilla (Manilkara zapota) acidic thaumatin-like protein in comparison with allergenic plant TLPs

Thaumatin-like proteins (TLPs) belong to the pathogenesis-related family (PR-5) of plant defense pro-
teins. TLPs from only 32 plant genera have been identified as pollen or food allergens. IgE epitopes on
allergens play a central role in food allergy by initiating cross-linking of specific IgE on basophils/mast
cells. A comparative analysis of pollen- and food-allergenic TLPs is lacking. The main objective of this
investigation was to study the structural and allergenicity features of sapodilla (Manilkara zapota) acidic
TLP (TLP 1) by in silico methods. The allergenicity prediction of composite sequence of sapodilla TLP 1
(NCBI B3EWX8.1, G5DC91.1) was performed using FARRP, Allermatch and Evaller web tools. A homology
model of the protein was generated using banana TLP template (1Z3Q) by HHPRED-MODELLER. B-cell lin-
ear epitope prediction was performed using BCpreds and BepiPred. Sapodilla TLP 1 matched significantly
with allergenic TLPs from olive, kiwi, bell pepper and banana. IgE epitope prediction as performed using
AlgPred indicated the presence of 2 epitopes (epitope 1: residues 36–48; epitope 2: residues 51–63), and
a comprehensive analysis of all allergenic TLPs displayed up to 3 additional epitopes on other TLPs. It
can be inferred from these analyses that plant allergenic TLPs generally carry 2–3 IgE epitopes. ClustalX
alignments of allergenic TLPs indicate that IgE epitopes 1 and 2 are common in food allergenic TLPs, and
IgE epitopes 2 and 3 are common in pollen allergenic TLPs; IgE epitope 2 overlaps with a portion of the
thaumatin family signature. The secondary structural elements of TLPs vary markedly in regions 1 and
2 which harbor all the predicted IgE epitopes in all food and pollen TLPs in either of the region. Further,
based on the number of IgE epitopes, food TLPs are grouped into rosid and non-rosid clades. The number
and distribution of the predicted IgE epitopes among the allergenic TLPs may explain the specificity of
food or pollen allergy as well as the varied degree of cross-reactivity among plant foods and/or pollens.