Biophysical Society Thematic Meeting

Biophysics in the Understanding, Diagnosis, and Treatment of Infectious Diseases Speaker Abstracts

Inhibition of Parasitic Farnesyl Diphosphate Synthases (FPPS)

Sandra B. Gabelli, Srinivas Aripirala, William Hong, Sweta Maheshwari, Sergio H. Szajnman,

Juan B. Rodriguez, Eric Oldfield,

Mario Amzel

Johns Hopkins University School of Medicine, Baltimore, MD, USA.

Farnesyl diphosphate synthase (FPPS), an essential enzyme involved in the biosynthesis of

sterols (cholesterol in humans and ergosterol in yeasts, fungi and trypanosomatid parasites) as

well as in protein prenylation, has been identified as a possible target for antiparasitic drug

development. FPPS is inhibited by bisphosphonates, a class of drugs used in humans to treat

diverse bone-related diseases. The development of bisphosphonates as antiparasitic compounds

targeting FPPS is being considered an important route for therapeutic intervention. X-ray

crystallographic and calorimetric studies of complexes of FPPS from Trypanosoma cruzi (the

etiologic agent of American trypanosomiasis; Chagas disease) and Leishmania major (the

causative agent of cutaneous leishmaniasis) are used to characterize binding of bisphosphonates

as potential therapeutic inhibitors of these enzymes. Calorimetric studies showed that binding of

bisphosphonates to these enzymes is entropically driven suggesting that one route for design may

involve increasing specific interaction of the compounds for the parasitic FPPSs to compensate

for the unfavorable enthalpy. Comparison of the structures of TcFPPS and LmFPPS to the

human FPPS provides new information for the design of bisphosphonates more specific for

inhibition of the parasitic FPPS.

Using Molecular Biophysics to Understand Plasmodium Actin Dynamics and Cell Motility

Ross Douglas

, Misha Kudryashev

1,2

, Marek Cyrklaff

, Freddy Frischknecht

University of Heidelberg Medical School, Heidelberg, Germany,

Current address: Biozentrum,

University of Basel, Basel, Switzerland.

Plasmodium

is the causative agent of malaria, a devastating tropical disease. Sporozoites, the

infectious forms transmitted by mosquitoes, are deposited in the skin of a mammalian host

during probing for a blood meal and rely on high motility speeds (approximately 1-3 µm/s) to

exit from the dermis into blood capillaries. Sporozoites display an uncommon form of

locomotion known as gliding motility, whereby the force of an actin-myosin motor is transmitted

through associated transmembrane adhesins to the substrate surface. Unlike its mammalian

counterparts,

Plasmodium

actin filaments appear to be inherently unstable and undergo rapid

turnover; with this dynamism being crucial for parasite motility. We use advanced microscopy,

biophysical methods and molecular genetics to probe sporozoite motility and to understand the

nature of actin dynamics in this process. Actin chimeras (whereby different regions were

swapped between mammalian and

Plasmodium

forms) were introduced into the parasite genome,

replacing the

actin 1

gene. We identified subdomain 4 of actin as an important contributor

towards parasite motility, as the respective chimera failed to efficiently invade the insect’s

salivary glands and showed aberrant ‘stop-go’ motility pattern. Further, these observations

emphasize the importance of this region in (un)stable filament dynamics.