Darya Tsibulskaya1* and Milan Kojić1
1Institute of Virology, Vaccines and Sera “Torlak”, Belgrade, Serbia
2650460 [at] gmail.com
Abstract
Autoaggregation is the ability of identical bacterial cells to adhere to each other, which is important for colonization, kin and kind recognition, and bacterial survival.
There is a group of aggregation factors in lactic acid bacteria that have several distinctive features: these are large proteins with a molecular mass greater than 150 kDa, containing an N-terminal signal sequence and an LPXTG-like cell wall anchor domain, as well as a different number of repetitive domains. These aggregation-promoting proteins are also called/known as Snow-flake Forming Collagen Binding Aggregation Factors (SFCBAF) due to their unique aggregation phenotype (PMIDs: 22182285, 29018422, 25955159, 30027759, 38014957). Predictions for different members of this group (predicted by the InterPro program) indicate a varying number and, in some cases, different compositions of repetitive domains.
Comparison of the predicted structures of known aggregation factors (AggL from Lactococcus lactis; AggE from Enterococcus faecium; AggLb from Lacticaseibacillus paracasei; AggLr from Lactococcus raffinolactis; and AggA from Tetragenococcus halophilus) using AlphaFold2 revealed structural similarities, which may explain the similar phenotype despite low identity (e.g., AggLb is identical to AggA at 21.73% and AggL at 41.14%, while AggA is identical to AggL at 32.43%). The structure itself resembles a shoe-like structure: with a heel and a sole in the form of a loop, consisting of 6-7 adhesion domains superfamily (InterPro: IPR008966). The most structurally dissimilar among them is AggLb, which is the largest of the described aggregation factors of this type and has a greater number of repeats in the second half of the protein compared to other members of this group. The calculation of electrostatic potential shows that the protein surfaces predominantly have negative potential, which is consistent with previously shown data for the AggLb protein, where the strain producing AggLb demonstrated higher affinities for chloroform and a lower percentage of adhesion to ethyl acetate, indicating that AggLb is able to provide strong electron-donor and weaker electron-acceptor features to the bacteria.
In summary, this research enhances our comprehension of the structure of aggregation factors in lactic acid bacteria.
Keywords: AlphaFold2, autoaggregation, SFCBAF.
Acknowledgement: This research was supported by the Ministry of Science, Technological Development and Innovation, Republic of Serbia, Contract no. 451-03-66/2024-03/ 200177.