Name: Jan Saras
PI: Mowbray/Jones (SLU/UU)
Project: Structural studies on membrane protein receptors
Gender: M
Actual starting date: 1 August, 1997
Administrative starting date: 1 July, 1997
The aim of the present study is to determine the three dimensional structure of a member of the Band 4.1 superfamily, both with and without physiologically relevant ligands.
Background
Band 4.1 is an erythrocyte membrane protein that, via its amino terminal domain of 30 kDa, can interact with acidic phospholipids in the plasma membrane as well as with the transmembrane proteins Glycophorin C and p55, the latter a membrane-associated guanylate kinase homologue (MAGUK). The C-terminal part of Band 4.1 interacts with actin/spectrin, and thus Band 4.1 provides a link between the plasma membrane and the cytoskeleton.
A group of proteins with sequence homology to Band 4.1, the Band 4.1 superfamily, has been identified. Many of these proteins have been found to localise to membranes at various adhesion structures and are thought to connect the cytoskeleton to the plasma membrane. Members of the superfamily include the ERM (ezrin, radixin, moesin) subfamily and talin. These proteins have, like Band 4.1, been shown to interact with acidic phospholipids. A number of reports indicate that proteins of this class are directly involved in signal transduction pathways. Merlin, another member of the Band 4.1 superfamily, was identified as a tumour suppressor (NF2). Most information is available concerning Band 4.1 itself, and it is therefore the primary target for this crystallography project.
Band 4.1 and Malaria
Band 4.1 has been shown to be important for the infection of human erythrocytes with the malaria parasite (Plasmodium falciparum). The hereditary haemolytic anaemia elliptocytosis has been coupled to resistance against malaria. The mutations (deletions) causing the condition in these patients are found in the genes of Band 4.1 or Glycophorin C. p55 is also absent in erythrocytes from these patients, suggesting that a functional complex between the three proteins is important for infection. Recently, it has become clear that the invasion (but not binding) of the parasite is reduced in human erythrocytes lacking Band 4.1. Furthermore, the parasite expresses a protein, MESA, that directly interacts with Band 4.1. Investigation of how the parasite interacts with the plasma membrane of the erythrocyte, and penetrates it, is of great biological significance and may lead to development of drugs against malaria as well as of methods for drug delivery. The data discussed here indicate that Band 4.1 has an important role in this mechanism and attempts to obtain structural and functional information of Band 4.1 are therefore highly warranted. The molecular mechanism behind the function of proteins of the Band 4.1 superfamily is generally unknown and solving the three dimensional structure of any family member will give invaluable information regarding how these proteins interact with the plasma membrane as well as with other proteins.
Recombinant expression and crystallisation
Several proteins of the Band 4.1 superfamily have been expressed as recombinant proteins in bacterial systems and in insect cells. We are currently making constructs for expression of Band 4.1, and functional fragments of it, in both these systems. We will purify the recombinant proteins and attempt to crystallise them alone and in complex with ligands such as phospholipids or peptides derived from Glycophorin C.
Latest update at 9 March, 1998.