1 / 18

Biochemistry of Plasmodium

Biochemistry of Plasmodium. Mark F. Wiser. http://www.tulane.edu/~wiser/malaria/. Sources of Amino Acids. De Novo Synthesis CO 2 fixation (ala, asp, glu) little incorporated into protein Host Plasma  uptake of all amino acids in vitro growth requires ile, met, cys, gln, glu

bonifacy
Télécharger la présentation

Biochemistry of Plasmodium

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Biochemistry of Plasmodium Mark F. Wiser http://www.tulane.edu/~wiser/malaria/

  2. Sources of Amino Acids • De Novo Synthesis • CO2 fixation (ala, asp, glu) • little incorporated into protein • Host Plasma •  uptake of all amino acids • in vitro growth requires ile, met, cys, gln, glu • Digestion of Host Hemoglobin

  3. Hemoglobin • 95% of total erythrocyte protein • very abundant (340 mg/ml or approximately 5 mM) • 60-80% is degraded during erythrocytic stage • 110 g (of 750 total) is consumed in 48 hrs at 20% parasitemia

  4. Endocytosis of Host Cytoplasm cytostome food vacuole pinocytosis (rings)

  5. The Food VacuoleA Specialized Lysosome ATP hemoglobin digestion H+ (pH 5-5.4) ADP • Food Vacuole Proteases • plasmepsins I - IV (acid) • falcipains I - III (thiol) • falcilysin (metallo) • Absent: • other acid hydrolases Endocytic Pathway parasite cytoplasm

  6. Proteases Mediate the Catabolism of Proteins • proteases (aka peptidases) break the peptide bonds that hold amino acids together • exopeptidases remove amino acids sequentially from either N- or C-terminus • endopeptidases cleave between ‘specific’ residues within polypeptide chain

  7. Initial plasmepsin cleavage is specificand leads to a destabilization of hemoglobin • native Hb is cleaved between Phe-33 and Leu-34 ( chains) • ‘hinge region’ • conserved • important for tetramer stability • the large globin fragments dissociate • heme is released • globin fragments are susceptible to further proteolysis a-F33/L34 í

  8. hemoglobin amino acids plasmepsin aminopeptidase large globin fragments heme + di-peptides falcipain plasmepsin medium fragments (~20 amino acids) small peptides (6-8 amino acids) falcilysin aminopeptidase amino acids Hemoglobin Digestion is an Ordered Process dipeptidyl aminopeptidase

  9. Membrane Transport • Channel proteins (hydrophilic pores) • Carrier proteins • substrate specific • most require energy • ATPase or gradients • 6 amino acid transporters identified in Plasmodium genome (location?) • ABC transporters also important for amino acid transport

  10. ABC Transporter Super Family • large and ubiquitous gene family • defined by ATP-Binding Cassette • transports a wide variety of substrates • aka Multi-Drug Resistance (MDR) • Pfmdr-1 protein localized to food vacuole • Pfmdr-1 complements yeast ste6 gene • ste6 exports mating factor • 12 residue peptide

  11. ATP H+ ADP The Food VacuoleA Specialized Lysosome hemoglobin proteins plasmepsin globin fragments heme + amino acids falcipain plasmepsin falcilysin • ABC transporter associated with food vacuole • amino-peptidase activities in parasite cytoplasm amino- peptidase ATP Pfmdr-1? amino acids small fragments (6-8 amino acids) ? ADP

  12. Free Heme is Toxic • heme destabilizes and lyses membranes • hydrolases released into parasite cytoplasm • parasite dies • Possible Detoxification Mechanisms • heme  hemozoin (malaria pigment) • H2O2 mediated degradation • GSH mediated degradation • heme oxygenase (P.b. and P.k. only)

  13. Hemozoin = b-Hematin b-hematin heme

  14. b-hematin forms insoluble crystals 'biocrystallization' or 'biomineralization'

  15. Pigment Formation • biocrystallization mechanism unknown • b-hematin can form spontaneously (harsh conditions) • lipid bodies can promote the process • derived from PVM • potential heme detoxification protein recently described • unique to Plasmodium species • binds 2-3 heme groups with high affinity (80 nM) • exported to host cytoplasm and taken up into food vacuole • heme biocrystallization inhibited by chloroquine and other anti-malarials

  16. The Food VacuoleA Specialized Lysosome ATP hemoglobin H+ plasmepsin Fe2+ O2 ADP globin fragments Fe3+ heme + amino acids -O2 O2 falcipain plasmepsin falcilysin ? • iron oxidized after release from Hb • oxidation promotes formation of ROI • oxidative stress amino- peptidase hemozoin ATP small fragments (6-8 amino acids) Pfmdr-1? ADP

  17. The Food VacuoleA Specialized Lysosome ATP hemoglobin H+ plasmepsin Fe2+ O2 ADP globin fragments Fe3+ heme + amino acids -O2 O2 falcipain plasmepsin falcilysin ? superoxide dismutase? amino- peptidase H2O2 hemozoin ATP catalase? small fragments (6-8 amino acids) amino acids Pfmdr-1? H2O + O2 ADP

More Related