Sheila Hollingshead

Bio: Sheila Hollingshead is an academic researcher. The author has contributed to research in topics: Glycoside & Alkaline hydrolysis (body disposal). The author has an hindex of 4, co-authored 4 publications receiving 101 citations.

On the surface coat and flagellar adhesion in trypanosomes.

Abstract: Pathogenic trypanosomes in their bloodstream phase have a smooth and compact coat 12-15 nm thick enveloping the entire surface membrane of the body and flagellum. In the sleeping-sickness trypanosome Trypanosoma rhodesiense this coat is absent from the stages of development in the midgut of the tsetse-fly vector and from their counterparts obtained by cultivation of the trypanosome in vitro. In the salivary glands of the vector, however, the coat is reacquired as the trypanosomes transform from epimastigote forms into the metacyclic stage which is infective to the mammalian host. This loss and acquisition of the surface coat can be correlated with the cyclical changes in net surface charge on the trypanosome which have been observed by other workers. The trypanosome populations of successive relapses in the blood are known to differ in their surface antigens (agglutinogens) and the loss of antigenic identity detected when any of these populations are put into culture indicates that these variable antigens are located in the surface coat. It is suggested that the coat in bloodstream trypanosomes constitutes a replaceable surface which, after being replaced, enables the trypanosome to escape the effects of host antibodies. The coat is therefore an adaptation to life in the bloodstream. Reacquisition of the surface coat by the metacyclic trypanosome after development in the vector may reflect reversion to a ‘basic’ antigenic type at this stage, preparatory to invading the blood of the mammalian host. The surface coat may be removed by the wide-spectrum proteolytic enzyme pronase, and this fact together with evidence from pH/mobility relationships and chemical analysis of the variable antigens suggest that the coat is basically proteinaceous. The coat may facilitate pinocytosis by binding proteins at sites within the pocket surrounding the base of the flagellum. In the non-pathogenic trypanosome T. lewisi a more diffuse filamentous coat is present in bloodstream forms and absent from culture forms. This trypanosome is said to carry a negative charge in both bloodstream and culture phases, so it seems likely that the nature of the coat in T. lewisi is different from that found in the pathogenic trypanosomes. In all these trypanosomes the flagellar membrane adheres to the surface membrane of the body throughout the life-cycle. Along the zone of adhesion lies a regular row of junctional complexes of the macula adherens type which, it is argued, serve in attachment. These attachments persist regardless of changes in the intervening cell surfaces.

Separation of trypanosomes from the blood of infected rats and mice by anion-exchangers

Abstract: SEPARATION of the bloodstream forms of trypanosomes from the blood of infected animals has so far been difficult, especially in the case of Trypanosoma congolense. Even the most satisfactory method—defibrination of the blood followed by centrifugation on a sucrose gradient1—has the disadvantage of usually being applicable only to small volumes of blood, because of the high gradient volume to blood ratio (at least 6 to 1).

Polymorphism and mitochondrial activity in sleeping sickness trypanosomes

Abstract: surface between the AB corner and the GH corner and are approximately related by the pseudo-dyad axis of symmetry named dyad 1 by Cullis et al. 4• However, the xenon atom in the oc-chain lies nearer the GH corner and thPt in the f3-chain closer to the AB corner. At first it might appear surprising that the xenon positions in the two chains are different from one another, and not the same as in myoglobin. The AB corners of the etand f3-chains differ in both the sequence and tho number of residues they contain, giving rise to structurally different environments. The amino-acid sequences in the GH corners are also different, though here the two chains are of equal length. It should also be noted that the amino-acid sequences of myoglobin• and haemoglobin are quite different. Any change in atomic distribution near a cavity could easily change the electronic interaction with xenon towards an energetically unfavourable state. The exact analysis of the xenon sites will have to await determination of the haemoglobin structure at high resolution. On the basis of Perutz's tentative atomic model of haemoglobin', the nearest neighbours of both xenon atoms are valine, leucine and pheny lalanine. This complex is presumably stabilized, as in myoglobin, by dipoleand quadrupole-induced dipole and quadrupole moments and London interactions. A theoretical investigation by Kittel and Shore8 of xenon polarizability has shown that the quadrupolar (as well as the dipolar) polarizability is particularly high, thus favouring binding in situations like this where one might not otherwise expect it. An analysis of the change in protein-bound water between haemoglobin and the haemoglobin-xenon complex by a microwave t echnique showed an increase of protein-bound water, due to the presence of xenon. Any attempts to demonstrate this directly by X-ray methods must also await the fina l analysis of haemoglobin at high resolution, but changes in the charge distribution caused by xenon atoms located close to the surface of the molecule could account for tho increase in bound water. I thank Dr. M. F. Porutz for his advice and use of his structural data of haemoglobin. This work was supported in part by the U.S. Public Health Service grant NB 03625 to R. M. Featherstone, chairman, Department of Pharmacology, University;,.of California Medical Center, San Francisco. 1 Schoenborn, B. P., Watson, H . C., and Kendrew, ;r, C., Nature, 207, 28 (1965). ' Cullen, S., and Cross, E., Scie11C

Cell Biology of Trypanosoma cruzi

Abstract: Publisher Summary Among the protozoa of the Trypanosomatidae family, a large number of species represent agents of diseases, such as Chagas' disease. This chapter reviews some aspects of the cell biology of Trypanosoma cruzi, giving emphasis to those aspects related to the ultrastructure of pathogenic protozoa. Protozoa of the Trypanosomatidae family show, during their, life cycle, several forms which can be easily identified by light microscopy in Giemsa-stained preparations. The chapter also explains the life cycle of T. cruzi. In the life cycle of T. cruzi, there are forms which are able to divide. There is one form, considered to be highly differentiated and responsible for the infectivity of these protozoa, which does not divide. It is highlighted that the trypomastigote form can transform into a rounded form which possesses a free flagellum. This form, which appears in the stomach, is able to transform into either short epimastigotes that start a process of multiplication in the intestinum or into long epimastigotes which move to the more posterior region of the digestive tract of the bug. Cell surface is also emphasized in the chapter.