Glycolipids as potential binding sites for HIV: topology in the sperm plasma membrane in relation to the regulation of membrane fusion

Characterization and distribution of HIV-infected cells in semen

Semen is a known vector for both human immunodeficiency virus (HIV) infection and transmission. However, the distribution and characteristics of HIV-infected cells in semen remain unclear. Investigating the possibility of transmission through the spermatozoon in semen is of great clinical significance to improve the strategies for exposure prevention and assisted reproduction for HIV-infected partners. Twenty-six HIV-infected patients, including twelve treatment-naïve (TN) patients and fourteen antiretroviral treated (ART) patients, were enrolled in this study. HIV p24 protein in spermatozoa was detected using imaging flow cytometry and immunohistochemistry, and HIV RNA was identified using next-generation RNAscope in situ hybridization. Additionally, we described the rates of HIV-positive spermatozoon and CD4⁺ T lymphocytes in semen, and found that p24⁺ spermatozoon were mainly CD4 negative regardless of whether the patients received ART. Of note, p24-positive cells in semen are predominantly spermatozoa, and we confirmed that motile spermatozoa carried HIV into peripheral blood mononuclear cells of healthy men in vitro. Our findings provide evidence regarding the risk of HIV-infected spermatozoa.

Potential for Virus Endogenization in Humans through Testicular Germ Cell Infection: the Case of HIV

Viruses have colonized the germ line of our ancestors on several occasions during evolution, leading to the integration in the human genome of viral sequences from over 30 retroviral groups and a few nonretroviruses. Among the recently emerged viruses infecting humans, several target the testis (e.g., human immunodeficiency virus [HIV], Zika virus, and Ebola virus). Here, we aimed to investigate whether human testicular germ cells (TGCs) can support integration by HIV, a contemporary retrovirus that started to spread in the human population during the last century. We report that albeit alternative receptors enabled HIV-1 binding to TGCs, HIV virions failed to infect TGCs in vitro Nevertheless, exposure of TGCs to infected lymphocytes, naturally present in the testis from HIV+ men, led to HIV-1 entry, integration, and early protein expression. Similarly, cell-associated infection or bypassing viral entry led to HIV-1 integration in a spermatogonial cell line. Using DNAscope, HIV-1 and simian immunodeficiency virus (SIV) DNA were detected within a few TGCs in the testis from one infected patient, one rhesus macaque, and one African green monkey in vivo Molecular landscape analysis revealed that early TGCs were enriched in HIV early cofactors up to integration and had overall low antiviral defenses compared with testicular macrophages and Sertoli cells. In conclusion, our study reveals that TGCs can support the entry and integration of HIV upon cell-associated infection. This could represent a way for this contemporary virus to integrate into our germ line and become endogenous in the future, as happened during human evolution for a number of viruses.IMPORTANCE Viruses have colonized the host germ line on many occasions during evolution to eventually become endogenous. Here, we aimed at investigating whether human testicular germ cells (TGCs) can support such viral invasion by studying HIV interactions with TGCs in vitro Our results indicate that isolated primary TGCs express alternative HIV-1 receptors, allowing virion binding but not entry. However, HIV-1 entered and integrated into TGCs upon cell-associated infection and produced low levels of viral proteins. In vivo, HIV-1 and SIV DNA was detected in a few TGCs. Molecular landscape analysis showed that TGCs have overall weak antiviral defenses. Altogether, our results indicate that human TGCs can support HIV-1 early replication, including integration, suggesting potential for endogenization in future generations.

Viruses in the reproductive tract: On their way to the germ line?

Studies of vertebrate genomes have indicated that all species contain in their chromosomes stretches of DNA with sequence similarity to viral genomes. How such 'endogenous' viral elements (EVEs) ended up in host genomes is usually explained in general terms such as 'they entered the germ line at some point during evolution'. This seems a correct statement, but is also rather imprecise. The vast number of endogenous viral sequences suggest that common routes to the 'germ line' may exist, as relying on chance alone may not easily explain the abundance of EVEs in modern mammalian genomes. An increasing number of virus types have been detected in human semen and a growing number of studies have reported on viral infections that cause male infertility or subfertility and on viral infections that threaten in vitro fertilisation practices. Thus, it is timely to survey the pathway(s) that viruses can use to gain access to the human germ line. Embryo transfer and semen quality studies in livestock form another source of relevant information because virus infection during reproduction is clearly unwanted, as is the case for the human situation. In this review, studies on viruses in the male and female reproductive tract and in the early embryo will be discussed to propose a plausible viral route to the mammalian germ line.

Sperm can act as vectors for HIV-1 transmission into vaginal and cervical epithelial cells

PROBLEM

Sperm are the major cells in semen. Human sperm possess a number of HIV-1 gp120 binding ligands including sulfogalactosylglycerolipid (SGG). However, the mechanisms of how sperm capture HIV-1 onto their surface are unclear. Furthermore, the ability of sperm to deliver HIV-1 to vaginal/cervical epithelial cells lining the lower female reproductive tract, as a first step in HIV-1 transmission, needs to be determined.

METHOD OF STUDY

Sperm from healthy donors were incubated with dual-tropic HIV-1_CS204 (clinical isolate), and virus capture was determined by p24 antigen ELISA. The involvement of SGG in HIV-1 capture was assessed by determining K_d values of HIV-1 gp120-SGG binding as well as computational docking of SGG to the gp120 V3 loop. The ability of sperm-associated HIV-1 to infect peripheral blood mononuclear cells (PBMCs) and TZM-bl indicator cells was determined. Lastly, infection of vaginal (Vk2/E6E7), ectocervical (Ect1/E6E7), and endocervical (End1/E6E7) epithelial cells mediated by HIV-1-associated sperm was evaluated.

RESULTS

Sperm were able to capture HIV-1 in a dose-dependent manner, and the capture reached a maximum within 5 minutes. Captured HIV-1, however, could be removed from sperm by Percoll-gradient centrifugation. Affinity of gp120 for SGG was substantial, implicating sperm SGG in HIV-1 capture. Sperm-associated HIV-1 could productively infect PBMCs and TZM-bl cells, and was capable of being transmitted into vaginal/cervical epithelial cells.

CONCLUSION

Sperm are able to capture HIV-1, which remains infectious and is able to be transmitted into vaginal/cervical epithelial cells, a result indicating the importance of sperm in HIV transmission.

Properties, metabolism and roles of sulfogalactosylglycerolipid in male reproduction

Sulfogalactosylglycerolipid (SGG, aka seminolipid) is selectively synthesized in high amounts in mammalian testicular germ cells (TGCs). SGG is an ordered lipid and directly involved in cell adhesion. SGG is indispensable for spermatogenesis, a process that greatly depends on interaction between Sertoli cells and TGCs. Spermatogenesis is disrupted in mice null for Cgt and Cst, encoding two enzymes essential for SGG biosynthesis. Sperm surface SGG also plays roles in fertilization. All of these results indicate the significance of SGG in male reproduction. SGG homeostasis is also important in male fertility. Approximately 50% of TGCs become apoptotic and phagocytosed by Sertoli cells. SGG in apoptotic remnants needs to be degraded by Sertoli lysosomal enzymes to the lipid backbone. Failure in this event leads to a lysosomal storage disorder and sub-functionality of Sertoli cells, including their support for TGC development, and consequently subfertility. Significantly, both biosynthesis and degradation pathways of the galactosylsulfate head group of SGG are the same as those of sulfogalactosylceramide (SGC), a structurally related sulfoglycolipid important for brain functions. If subfertility in males with gene mutations in SGG/SGC metabolism pathways manifests prior to neurological disorder, sperm SGG levels might be used as a reporting/predicting index of the neurological status.

Innate and adaptive immune responses in male and female reproductive tracts in homeostasis and following HIV infection

The male and female reproductive tracts are complex microenvironments that have diverse functional demands. The immune system in the reproductive tract has the demanding task of providing a protective environment for a fetal allograft while simultaneously conferring protection against potential pathogens. As such, it has evolved a unique set of adaptations, primarily under the influence of sex hormones, which make it distinct from other mucosal sites. Here, we discuss the various components of the immune system that are present in both the male and female reproductive tracts, including innate soluble factors and cells and humoral and cell-mediated adaptive immunity under homeostatic conditions. We review the evidence showing unique phenotypic and functional characteristics of immune cells and responses in the male and female reproductive tracts that exhibit compartmentalization from systemic immunity and discuss how these features are influenced by sex hormones. We also examine the interactions among the reproductive tract, sex hormones and immune responses following HIV-1 infection. An improved understanding of the unique characteristics of the male and female reproductive tracts will provide insights into improving clinical treatments of the immunological causes of infertility and the design of prophylactic interventions for the prevention of sexually transmitted infections.

Adding glycolipid functionality to model membranes--phase behaviour of a synthetic glycolipid in a phospholipid membrane

Glycolipid phase behaviour is less well understood than for many phospholipids, but due to their structural and functional diversity, glycolipids represent an important group of amphiphiles from which biological function is derived. Here we have incorporated a synthetic glycolipid in binary mixtures with DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine) into giant unilamellar vesicles (GUVs) at biologically relevant concentrations and observed the phase behaviour of the lipid mixtures for a range of glycolipid concentrations. At low concentrations, the glycolipid is fully dispersed in the GUV membrane. At glycolipid molar concentrations above 10%, the formation of lipid tubules is observed, and is consistent with the formation of a columnar lipid phase. Lipid tubules are observed in aqueous and oil solvents, suggesting that both hexagonal and inverted hexagonal lipid arrangements can be formed. This work may offer insights into the biological function of glycolipids and the challenges in formulating them for use in industrial applications.

HIV infection of the male genital tract--consequences for sexual transmission and reproduction

Despite semen being the main vector of human immunodeficiency virus (HIV) dissemination worldwide, the origin of the virus in this bodily fluid remains unclear. It was recently shown that several organs of the male genital tract (MGT) are infected by HIV/simian immunodeficiency virus (SIV) and likely to contribute to semen viral load during the primary and chronic stages of the infection. These findings are important in helping answer the following questions: (i) does the MGT constitute a viral reservoir responsible for the persistence of virus release into the semen of a subset of HIV-infected men under antiretroviral therapy, who otherwise show an undetectable blood viral load? (ii) What is the aetiology of the semen abnormalities observed in asymptomatic HIV-infected men? (iii) What is the exact nature of the interactions between the spermatozoa, their testicular progenitors and HIV, an important issue in the context of assisted reproductive techniques proposed for HIV-seropositive (HIV+) men? Answers to these questions are crucial for the design of new therapeutic strategies aimed at eradicating the virus from the genital tract of HIV+ men--thus reducing its sexual transmission--and for improving the care of serodiscordant couples wishing to have children. This review summarizes the most recent literature on HIV infection of the male genital tract, discusses the above issues in light of the latest findings and highlights future directions of research.

Galactosylceramide domain microstructure: impact of cholesterol and nucleation/growth conditions

Galactosylceramide (GalCer), a glycosphingolipid, is believed to exist in the extracellular leaflet of cell membranes in nanometer-sized domains or rafts. The local clustering of GalCer within rafts is thought to facilitate the initial adhesion of certain viruses, including HIV-1, and bacteria to cells through multivalent interactions between receptor proteins (gp120 for HIV-1) and GalCer. Here we use atomic force microscopy (AFM) to study the effects of cholesterol on solid-phase GalCer domain microstructure and miscibility with a fluid lipid 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) in supported lipid bilayers. Using "slow-cooled vesicle fusion" to prepare the supported lipid bilayers, we were able to overcome the nonequilibrium effects of the substrate (verified by comparison to results for giant unilamellar vesicles) and accurately quantify the dramatic effect of cholesterol on the GalCer domain surface area/perimeter ratio (A(D)/P) and DLPC-GalCer miscibility. We compare these results to a supported lipid bilayer system in which the bilayer is rapidly cooled (nonequilibrium conditions), "quenched vesicle fusion", and find that the microstructures are remarkably similar above a cholesterol mol fraction of approximately 0.06. We determined that GalCer domains were contained in one leaflet distal to the mica substrate through qualitative binding experiments with Trichosanthes kirilowii agglutinin (TKA), a galactose-specific lectin, and AFM of Langmuir-Blodgett deposited GalCer/DLPC supported lipid bilayers. In addition, GalCer domains in bilayers containing cholesterol rearranged upon tip-sample contact. Our results further serve to clarify why discrepancies exist between different model membrane systems and between model membranes and cell membranes. In addition, these results offer new insight into the effect of cholesterol and surrounding lipid on domain microstructure and behavior. Finally, our observations may be pertinent to cell membrane structure, dynamics, and HIV infection.

Chemokine receptor expression in the human ectocervix: implications for infection by the human immunodeficiency virus-type I

Human immunodeficiency virus-type 1 (HIV-1) is a sexually transmitted pathogen that can infect cells in the female reproductive tract (FRT). The mechanism of viral transmission within the FRT and the mode of viral spread to the periphery are not well understood. To characterize the frequency of potential targets of HIV infection within the FRT, we performed a systematic study of the expression of HIV receptors (CD4, galactosyl ceramide (GalCer)) and coreceptors (CXCR4 and CCR5) on epithelial cells and leucocytes from the ectocervix. The ectocervix is a likely first site of contact with HIV-1 following heterosexual transmission, and expression of these receptors is likely to correlate with susceptibility to viral infection. We obtained ectocervical tissue specimens from women undergoing hysterectomy, and compared expression of these receptors among patients who were classified as being in the proliferative or secretory phases of their menstrual cycle at the time of hysterectomy, as well as from postmenopausal tissues. Epithelial cells from tissues at early and mid-proliferative stages of the menstrual cycle express CD4, although by late proliferative and secretory phases, CD4 expression was absent or weak. In contrast, GalCer expression was uniform in all stages of the menstrual cycle. CXCR4 expression was not detected on ectocervical epithelial cells and positive staining was only evident on individual leucocytes. In contrast, CCR5 expression was detected on ectocervical epithelial cells from tissues at all stages of the menstrual cycle. Overall, our results suggest that HIV infection of cells in the ectocervix could most likely occur through GalCer and CCR5. These findings are important to define potential targets of HIV-1 infection within the FRT, and for the future design of approaches to reduce the susceptibility of women to infection by HIV-1.

Human immunodeficiency virus receptor and coreceptor expression on human uterine epithelial cells: regulation of expression during the menstrual cycle and implications for human immunodeficiency virus infection

Human immunodeficiency virus-1 (HIV-1) is primarily a sexually transmitted disease. Identification of cell populations within the female reproductive tract that are initially infected, and the events involved in transmission of infection to other cells, remain to be established. In this report, we evaluated expression of HIV receptors and coreceptors on epithelial cells in the uterus and found they express several receptors critical for HIV infection including CD4, CXCR4, CCR5 and galactosylceramide (GalC). Moreover, expression of these receptors varied during the menstrual cycle. Expression of CD4 and CCR5 on uterine epithelial cells is high throughout the proliferative phase of the menstrual cycle when blood levels of oestradiol are high. In contrast, CXCR4 expression increased gradually throughout the proliferative phase. During the secretory phase of the cycle when both oestradiol and progesterone are elevated, CD4 and CCR5 expression decreased whereas CXCR4 expression remained elevated. Expression of GalC on endometrial glands is higher during the secretory phase than during the proliferative phase of the menstrual cycle. Because epithelial cells line the female reproductive tract and express HIV receptors and coreceptors, it is likely that they are one of the first cell types to become infected. The hormonal regulation of HIV receptor expression may affect a woman's susceptibility to HIV infection during her menstrual cycle. Moreover, selective coreceptor expression could account for the preferential transmission of R5-HIV-1 strains to women. In addition, these studies provide evidence that the uterus, and potentially the entire upper reproductive tract, are important sites for the initial events involved in HIV infection.

Analysis of HIV-1 viral load in seminal plasma samples

BACKGROUND

With HIV-1-infected individuals now facing the prospect of relatively long and healthy lives, many discordant couples (where the male is HIV-1 seropositive) are seeking to have children. To assist reducing the risks of heterosexual and subsequent vertical transmission in this situation, quantification of HIV-1 viral load in seminal plasma may be effective as one of several measures to reduce the risk of infecting the mother during insemination, potentially providing a better indication of infectivity than blood plasma analysis.

OBJECTIVE(S)

To modify existing molecular methods for the purpose of analysing HIV-1 viral load in seminal plasma.

METHODS

Two commercial assays for HIV-1 RNA quantification were used to assess their sensitivity, specificity and precision for quantification of seminal plasma samples. Seminal plasma samples were prepared with an additional centrifugation step to aid removal of inhibitors to molecular assays.

RESULTS

Seminal plasma samples exhibited specificity of >95%, equivalent to that reported by the manufacturers of the commercial assays. With additional centrifugation, complete inhibition of 2/19 (10%) seminal plasma samples was observed using the RT-PCR assay, and inhibition was not apparent in the bDNA assay. Quantification of HIV-1 RNA in seminal plasma samples in both assays was equivalent to that observed in plasma samples and did not appear to be affected by the additional centrifugation step.

CONCLUSION

Minor modification of the RT-PCR assay procedure by additional centrifugation of seminal plasma improved the sensitivity of the assay. Inhibition was not apparent with the bDNA assay.

Assisted reproduction in HIV-1-serodifferent couples: the need for viral validation of processed semen

BACKGROUND

Many HIV-infected men and women have a strong desire for a child. Assisted reproductive technologies (ART) are an option for HIV-serodifferent couples to reduce the risk of HIV transmission from an infected man to the woman. Potential HIV contamination of selected spermatozoa after semen processing is an important issue in this context.

METHODS

HIV in processed semen obtained in our laboratory since 1995 were analysed. HIV RNA and DNA detection was performed in the selected spermatozoa of 125 men. HIV RNA was analysed in blood and semen plasma as well as HIV DNA in non-sperm cells.

RESULTS

HIV RNA and DNA were detected in the selected spermatozoa of eight and two men (6.4% and 1.6%), respectively. HIV RNA was detected with a median load of 5 copies/10(6) spermatozoa. Six of the eight men were untreated, one was taking nucleoside analogue therapy and one was on highly active antiretroviral treatment (HAART). HIV RNA detection was more likely to be positive in selected spermatozoa of men with high seminal plasma viral load. HIV RNA was detected in 26% and 11% of selected spermatozoa fractions when the seminal plasma load was > 10,000 copies/ml and 20-10,000 copies/ml, respectively, but in none when the seminal plasma tested negative.

CONCLUSION

Selected spermatozoa may be positive for HIV RNA detection even in treated patients. Viral validation of processed semen is necessary in ART programmes for serodifferent couples, particularly in men with only partially or poorly controlled HIV infection.

A novel soluble analog of the HIV-1 fusion cofactor, globotriaosylceramide (Gb(3)), eliminates the cholesterol requirement for high affinity gp120/Gb(3) interaction

We have analyzed the interaction of adamantyl Gb(3) (adaGb(3)), a semi-synthetic soluble analog of Gb(3), with HIV-1 surface envelope glycoprotein gp120. In this analog, which was orginally designed to inhibit verotoxin binding to its glycolipid receptor, Gb(3), the fatty acid chain is replaced with a rigid globular hydrocarbon frame (adamantane). Despite its solubility, adaGb(3) forms monolayers at an air-water interface. Compression isotherms of such monolayers demonstrated that the adamantane substitution resulted in a larger minimum molecular area and a more rigid, less compressible film than Gb(3). Insertion of gp120 into adaGb(3) monolayers was exponential whereas the gp120/Gb(3) interaction curve was sigmoidal with a lag phase of 40 min. Adding cholesterol into authentic Gb(3) monolayers abrogated the lag phase and increased the initial rate of interaction with gp120. This effect of cholesterol was not observed with phosphatidylcholine or sphingomyelin. In addition, verotoxin-bound adaGb(3) or Gb(3) plus cholesterol was recovered in fractions of comparable low density after ultracentrifugation through sucrose-density gradients in the presence of Triton X-100. The unique biological and physico-chemical properties of adaGb(3) suggest that this analog may be a potent soluble mimic of Gb(3), providing a novel concept for developing GSL-derived viral fusion inhibitors.

Sulfogalactosylglycerolipid is involved in human gamete interaction

Recent results from our laboratory have revealed the role of sulfogalactosylglycerolipid (SGG) in mouse sperm-zona pellucida (ZP) binding. In this report, we demonstrated the presence of SGG in Percoll-gradient centrifuged (PGC) human sperm by high performance thin layer chromatography with orcinol and Azure A staining, specific for glycolipids and sulfolipids, respectively. SGG in human PGC sperm was quantified by its affinity to Azure A to be 12-15 mol% of sperm lipids. Indirect immunofluorescence revealed that SGG existed on both live and aldehyde fixed human sperm in the head region. Pretreatment of human PGC sperm with affinity purified antiSGG Fab markedly inhibited sperm binding to the ZP in a concentration dependent manner, without any changes in the spontaneous acrosome rate or sperm motility parameters. Fluorescently labeled SGG liposomes also bound uniformly to isolated human ZP, while fluorescently labeled galactosylglycerolipid (GG, SGG's parental lipid) or phosphatidylserine (PS, negatively charged like SGG) liposomes did not. All of these results suggested the role of human sperm SGG in ZP binding.

The physical properties of glycosyl diacylglycerols. Calorimetric, X-ray diffraction and Fourier transform spectroscopic studies of a homologous series of 1,2-di-O-acyl-3-O-(beta-D-galactopyranosyl)-sn-glycerols

We have synthesized a homologous series of saturated 1,2-di-O-n-acyl-3-O-(beta-D-galactopyranosyl)-sn-glycerols with odd- and even-numbered hydrocarbon chains ranging in length from 10 to 20 carbon atoms, and have investigated their physical properties using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy. The DSC results show a complex pattern of phase behaviour, which in a typical preheated sample consists of a lower temperature, moderately energetic lamellar gel/lamellar liquid-crystalline (L(beta)/L(alpha)) phase transition and a higher temperature, weakly energetic lamellar/nonlamellar phase transition. On annealing at a suitable temperature below the L(beta)/L(alpha) phase transition, the L(beta) phase converts to a lamellar crystalline (L(c1)) phase which may undergo a highly energetic L(c1)/L(alpha) or L(c1)/inverted hexagonal (H(II)) phase transition at very high temperatures on subsequent heating or convert to a second L(c2) phase in certain long chain compounds on storage at or below 4 degrees C. The transition temperatures and phase assignments for these galactolipids are supported by our XRD and FTIR spectroscopic measurements. The phase transition temperatures of all of these events are higher than those of the comparable phase transitions exhibited by the corresponding diacyl alpha- and beta-D-glucosyl glycerols. In contrast, the L(beta)/L(alpha) and lamellar/nonlamellar phase transition temperatures of the beta-D-galactosyl glycerols are lower than those of the corresponding diacyl phosphatidylethanolamines (PEs) and these glycolipids form inverted cubic phases at temperatures between the lamellar and H(II) phase regions. Our FTIR measurements indicate that in the L(beta) phase, the hydrocarbon chains form a hexagonally packed structure in which the headgroup and interfacial region are undergoing rapid motion, whereas the L(c) phase consists of a more highly ordered, hydrogen-bonded phase, in which the chains are packed in an orthorhombic subcell similar to that reported for the diacyl-beta-D-glucosyl-sn-glycerols. A comparison of the DSC data presented here with our earlier studies of other diacyl glycolipids shows that the rate of conversion from the L(beta) to the L(c) phase in the beta-D-galactosyl glycerols is slightly faster than that seen in the alpha-D-glucosyl glycerols and much faster than that seen in the corresponding beta-D-glucosyl glycerols. The similarities between the FTIR spectra and the first-order spacings for the lamellar phases in both the beta-D-glucosyl and galactosyl glycerols suggest that the headgroup orientations may be similar in both beta-anomers in all of their lamellar phases. Thus, the differences in their L(beta)/L(c) conversion kinetics and the lamellar/nonlamellar phase properties of these lipids probably arise from subtly different hydration and H-bonding interactions in the headgroup and interfacial regions of these phases. In the latter case, such differences would be expected to alter the ability of the polar headgroup to counterbalance the volume of the hydrocarbon chains. This perspective is discussed in the context of the mechanism for the L(alpha)/H(II) phase transition which we recently proposed, based on our X-ray diffraction measurements of a series of PEs.

A Fourier-transform infrared study of the interaction between germ-cell specific sulfogalactosylglycerolipid and dimyristoylglycerophosphocholine

In this study, we investigated structural and dynamic changes of sulfogalactosylglycerolipid (SGG) and dimyristoylglycerophosphocholine (DMPC) in a liposomal system (SGG+DMPC, molar ratio 2:3) by Fourier-transform infrared (FTIR) spectroscopy. Cooling of the preheated SGG liposomes (5-65 degrees C) revealed that the liquid crystalline-to-gel phase transition was centered at 45 degrees C. SGG+DMPC liposomes showed a single phase transition at 28 degrees C. Spectral changes of the ester C&z. dbnd6;O groups of SGG and DMPC in the mixed liposomes indicated a decrease in their interfacial hydrogen bonding intermolecularly and with water. Analysis of SGG's symmetric and antisymmetric CH(2) stretching bands revealed that the insertion of DMPC into SGG bilayers increased the number of gauche conformers in SGG's hydrocarbon chains. Overall, the SGG+DMPC liposomes were homogeneous, with reduced interfacial hydrogen bonding and increased orientational and conformational disorder of SGG's hydrocarbon chains.

New insights into the interaction between the gp120 and the HIV receptor in human sperm (human.sperm/gp120/galactoglycerolipid/antigalactosylceramide/seminolip id/spermatogonia)

The human immunodeficiency virus (HIV) can infect some cell types which lack CD4. Galactosylceramide, a glycolipid present in the nervous system and colonic epithelial cells, has been implicated in the virus entry in these cells. Our data demonstrate that the HIV surface glycoprotein gp120 binds to the galactosyl-alkyl-acylglycerol (GalAAG), a glycolipid structurally related to galactosylceramide present on the surface membrane of the spermatozoa. In this paper, we review our previous data and further confirm the specificity of the interaction between this galactoglycerolipid and the gp120. Consistent with the structural similarity to galactosylceramide, the sperm GalAAG is capable of specifically binding the gp120. The specificity of the binding of antibodies antigalactosylceramide and the gp120 to the sperm extract and to the purified GalAAG fraction prepared from the same extract has been demonstrated utilizing an ELISA assay which favors sensitivity and specificity. Immunofluorescence and immunoelectron microscopy data show a different localization for the GalAAG and its sulfated form the seminolipid (SGalAAG). The GalAAG is preferentially localized in the equatorial segment and the middle piece of the sperm tail, while the seminolipid is widely distributed on the membrane of the spermatozoa. These data indicate that human sperm express on their surface membrane a glycolipid similar in structure to galactosylceramide, the receptor for HIV identified in the CD4 cells, that could function as a HIV receptor and possibly be implicated in its transmission.