Fibrillar Adhesins-Like Proteins

Shayan Ahmed, Jamia Millia Islamia, New Delhi

Understanding bacterial infection processes and defining relationships with commensal bacteria necessitates research into how bacteria interact with their hosts. The initial stage in bacterial infection is adhesion to the host cell. Anti-adhesion treatments that interfere with the adhesion process, typically by activating a humoral immune response, are an effective way to avoid infections. This approach has been frequently used to develop vaccines that target host binding proteins. A recent study sought to describe fibrillar adhesins across a diverse variety of bacterial phyla, as well as to find novel fibrillar adhesin-like (FA-like) proteins, in order to enhance our knowledge of host-bacterium interactions.

Fibrillar Adhesins and FA-Like Proteins

Fibrillar adhesins are long filamentous surface proteins with similar activities that are expressed by a diverse range of bacteria. Fibrillar adhesins have a role in biofilm formation and other cell-cell interactions, in addition to mediating connections between bacteria and host cells. Fibrillar adhesins have a role in biofilm formation and other cell-cell interactions, in addition to mediating connections between bacteria and host cells. The term “fibrillar adhesin” comes from the filamentous appearance of the proteins when examined under the electron microscope. Instead of numerous protein subunits present in pili or fimbriae, fibrillar adhesins are made up of vast arrays of domains in a single protein chain, frequently repeated in tandem. These domains are known as stalk domains because they serve as elongated rod-like structures that propel the protein’s functional portion, the sticky domain, towards the target host cell. So far, just a few fibrillar adhesins have been investigated, and they originate from a small number of species. 

The FA-like proteins are extracellular proteins, these possess an adhesive region usually at the protein terminus and a stalk-like region that forms a rigid rod-like structure. FA-like proteins also possess a surface anchoring motif or domain. FA-like proteins are made up of one or a few identical fibrillar chains, each of which has one monomer that extends the length of the fibril. Fibrillar adhesins appear to be made up of a small number of domain families, which makes computational identification easier.

Findings

The findings demonstrate the numerous adhesive and stalk domain combinations that exist in nature, as well as how common they are. The information could aid in the discovery of new fibrillar adhesins. Several sticky domains have been discovered in conjunction with various stalk domains. The presence of sticky domains at the N-terminus of Firmicutes FA-like proteins was among the most striking outcomes of the domain grammar study. It was also discovered that the relative location of several of the studied adhesion domains in FA-like proteins remains consistent. The taxonomic distribution of adhesive and stalk domains in Gram-positive bacteria revealed a wide range of distinct domains. The lack of knowledge about fibrillar adhesins is one explanation for the low variety of FA-like proteins in Gram-negative bacteria. Another explanation is that Gram-negative bacteria rely heavily on pili, or Outer Membrane Proteins, for host cell attachment and hence have fewer fibrillar adhesins.

Several adhesive domains are discovered to be repeated. Repeated adhesive domains may increase the avidity of binding to host cells. As a result, duplications of these domains may result in increased stalk length and binding efficiency. The need that a protein possesses a mix of recognized stalk and adhesive domains is the most significant restriction of our FA-like protein discovery approach. The discovery of FA-like proteins and related stalk and sticky domains in this study laid the groundwork for the discovery of other fibrillar adhesins. However, the knowledge obtained regarding fibrillar adhesins in this work will be useful in improving future identification of these proteins.

Also read: Unveiling the features of within-host dynamics in malaria

Source: Monzon, V., Lafita, A., & Bateman, A. (2021). Discovery of fibrillar adhesins across bacterial species. BMC genomics, 22(1), 550. https://doi.org/10.1186/s12864-021-07586-2

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About the Author: Shayan Ahmed is currently pursuing a Master of Science degree in Microbiology from the Department of Biosciences, Jamia Millia Islamia, New Delhi. His area of research interest lies in antibiotic resistance and associated molecular mechanisms. His recent work was focused on understanding colistin resistance patterns in the environment, particularly in water bodies.