Team:Technion Israel/S.Tar intro
Chemotaxis
is the movement of an organism in response to an external chemical stimulus The bacterial
chemotaxis system is characterized by specific responses, high sensitivity and a dynamic
range (1). This system enables bacteria to sense their immediate environment and
quickly adapt to changes in its chemical composition - fleeing from repellents and moving
towards attractants. The key to this system and the first link in the chain is the bacterial
chemoreceptor - a membrane protein that binds the effector and transduces the signal down
the line.
Despite its advantages this system is still rather limited, bacterial chemoreceptors have evolved
to sense specific materials that either benefit or harm the cell in some way. The specificity of
a receptor is determined by its ligand binding domain. This domain is the focus of project S.Tar.
Fig. 1: A bacterial sense of direction.
S.Tar
The S.Tar platform offers the means to decide what substance will trigger a chemotactic response- controlled chemotaxis. The base of our project and the source of our name is the Tar chemoreceptor, one of four E. coli receptors. By changing Tar’s ligand binding domain to that of other receptors or by mutating it we show that E. coli can be engineered to respond to completely new materials.
As a proof of concept we present two receptors:
1. PctA-Tar,
a chimera created by replacing the Tar LBD with that of the Pseudomonas receptor PctA.
2. Histamine-Tar,
a receptor created with the help of computational design - using 'Rosetta' bioinformatics
software suite to design mutations in the Tar receptor.
Our attempts did not end here, we also present two bold attempts to fuse a ligand binding
domain of human origin to Tar in order to induce chemotaxis towards
Estrogen hormone
and a novel lock and key system relies on
intein proteins
and is purpose is to disable chemotaxis until a specific substance “opens the door” - induces
intein splicing and enables chemotaxis.
We have created non-natural chemoreceptors, by modifying Tar’s ligand binding domain.
The main goal of project S.Tar was to design new chemoreceptors that do not exist
in nature. These new chemoreceptors were based on the Tar chemoreceptor.
Said chemoreceptor structure consists of three main regions: Ligand binding
domain (LBD), The HAMP domain and the MH bundle (2).
Fig. 3: Tar chemoreceptor structure.
Our project focused on altering the LBD region by using different tools and approaches
each designed to achieve a unique response. The three major approaches were as follows:
1. Tar-Chimeras: a hybrid receptor consisting of an LBD from different sources,
such as human and other bacteria, fused to the HAMP and MH of Tar. An example of these
hybrids: PctA-Tar and Narx-Tar.
2. Intein: A protein fused into the LBD that functions as an on/off mechanism
that allows the control of chemotaxis.
3. Rosetta: a computer software that helps with the design of new LBDs
that recognizes the ligand of your choice.
1. Bi, S. and Lai, L., 2015. Bacterial chemoreceptors and chemoeffectors. Cellular and Molecular Life Sciences, 72(4), pp.691-708.
2. BI, Shuangyu; LAI, Luhua. Bacterial chemoreceptors and chemoeffectors. Cellular and Molecular Life Sciences, 2015, 72.4: 691-708.
3. British Society for Immunology
