Biomedical subjects

Björn F C Kafsack

Publications and source records attributed to Björn F C Kafsack.

3 recordsLinked to original sources

PubMed2005

The opportunistic pathogen Toxoplasma gondii deploys a diverse legion of invasion and survival proteins.

Host cell invasion is an essential step during infection by Toxoplasma gondii, an intracellular protozoan that causes the severe opportunistic disease toxoplasmosis in humans. Recent evidence strongly suggests that proteins discharged from Toxoplasma apical secretory organelles (micronemes, dense granules, and rhoptries) play key roles in host cell invasion and survival during infection. However, to date, only a limited number of secretory proteins have been discovered, and the full spectrum of effector molecules involved in parasite invasion and survival remains unknown. To address these issues, we analyzed a large cohort of freely released Toxoplasma secretory proteins by using two complementary methodologies, two-dimensional electrophoresis/mass spectrometry and liquid chromatography/electrospray ionization-tandem mass spectrometry (MudPIT, shotgun proteomics). Visualization of Toxoplasma secretory products by two-dimensional electrophoresis revealed approximately 100 spots, most of which were successfully identified by protein microsequencing or matrix-assisted laser desorption ionization-mass spectrometry analysis. Many proteins were present in multiple species suggesting they are subjected to substantial post-translational modification. Shotgun proteomic analysis of the secretory fraction revealed several additional products, including novel putative adhesive proteins, proteases, and hypothetical secretory proteins similar to products expressed by other related parasites including Plasmodium, the etiologic agent of malaria. A subset of novel proteins were re-expressed as fusions to yellow fluorescent protein, and this initial screen revealed shared and distinct localizations within secretory compartments of T. gondii tachyzoites. These findings provided a uniquely broad view of Toxoplasma secretory proteins that participate in parasite survival and pathogenesis during infection.

Animals↗

PubMed2004

The novel coccidian micronemal protein MIC11 undergoes proteolytic maturation by sequential cleavage to remove an internal propeptide.

Host cell invasion is a key step in the life cycle of the intracellular parasite Toxoplasma gondii, the causative agent of toxoplasmosis. Attachment and invasion by this parasite is dependent on secretion of proteins from the micronemes, cigar-shaped organelles found in the apical end of the parasite. Although many of these proteins contain adhesive motifs suggestive of a role in parasite attachment, a growing subset of microneme proteins (MICs) do not possess adhesive sequences implying that they have alternative roles. We have identified a novel 16 kDa microneme protein, TgMIC11, that is conserved among several coccidian parasites. As it traffics through the secretory system, TgMIC11 is modified by two successive proteolytic events to remove an internal propeptide, resulting in the mature protein that consists of an alpha-chain and beta-chain tethered by a single disulfide bond. Dual staining immunofluorescence confirmed that TgMIC11 localises to the apical micronemes and, like other micronemal proteins, it is also secreted in a calcium dependent manner. This is the first microneme protein characterised to date in the phylum Apicomplexa that possesses this unique structure and undergoes maturation by removal of an internal propeptide.

Amino Acid Sequence↗

PubMed2003

Competition between two MHC binding registers in a single peptide processed from myelin basic protein influences tolerance and susceptibility to autoimmunity.

Experimental allergic encephalomyelitis (EAE) is an animal model for multiple sclerosis induced by stimulating myelin basic protein (MBP)-specific T cells. The MBP-specific repertoire in B10.PL mice is shaped by tolerance mechanisms that eliminate MBP121-150-specific T cells. In contrast, MBPAc1-11-specific T cells escape tolerance and constitute the encephalitogenic repertoire. To determine if this differential tolerance is caused by differences in the abundance of MBP epitopes generated by processing, MBP peptides were eluted from I-Au complexes and analyzed by mass spectrometry. Peptides were identified from both the NH2-terminal and MBP121-150 regions. Unexpectedly, MBPAc1-18 and Ac1-17, which contain the MBPAc1-11 epitope, were much more abundant than MBP121-150 peptides. The results demonstrate that competition between two I-Au binding registers, a low affinity register defined by MBPAc1-11 and a high affinity register defined by MBP5-16, prevents most of the NH2-terminal naturally processed peptides from binding in the MBPAc1-11 register. The small fraction of MBPAc1-18 bound in the MBPAc1-11 register is not sufficient to induce tolerance but provides a ligand for MBPAc1-11-specific T cells during disease. These results provide a basis for both the lack of tolerance to MBPAc1-11 and the ability of this epitope to become a target during autoimmunity.

Animals↗