Discovery and Characterization of an Endogenous CXCR4 Antagonist

CXCL12-CXCR4 signaling controls multiple physiological processes and its dysregulation is associated with cancers and inflammatory diseases. To discover as-yet-unknown endogenous ligands of CXCR4, we screened a blood-derived peptide library for inhibitors of CXCR4-tropic HIV-1 strains. This approach identified a 16 amino acid fragment of serum albumin as an effective and highly specific CXCR4 antagonist. The endogenous peptide, termed EPI-X4, is evolutionarily conserved and generated from the highly abundant albumin precursor by pH-regulated proteases. EPI-X4 forms an unusual lasso-like structure and antagonizes CXCL12-induced tumor cell migration, mobilizes stem cells, and suppresses inflammatory responses in mice. Furthermore, the peptide is abundant in the urine of patients with inflammatory kidney diseases and may serve as a biomarker. Our results identify EPIX4 as a key regulator of CXCR4 signaling and introduce proteolysis of an abundant precursor protein as an alternative concept for chemokine receptor regulation

Structure-Based Design of Non-Natural Amino Acid Inhibitors of Amyloid Fibrillation

Many globular and natively disordered proteins can convert into amyloid fibers. These fibers are associated with numerous pathologies1 as well as with normal cellular functions2,3, and frequently form during protein denaturation4,5. Inhibitors of pathological amyloid fibers could serve as leads for therapeutics, provided the inhibitors were specific enough to avoid interfering with normal processes. Here we show that computer-aided, structure-based design can yield highly specific peptide inhibitors of amyloid formation. Using known atomic structures of segments of amyloid fibers as templates, we have designed and characterized an all D-amino acid inhibitor of fibrillation of the tau protein found in Alzheimer’s disease, and a non-natural L-amino acid inhibitor of an amyloid fiber that enhances sexual transmission of HIV. Our results indicate that peptides from structure-based designs can disrupt the fibrillation of full-length proteins, including those like tau that lack fully ordered native structures.We thank M.I. Ivanova, J. Corn, T. Kortemme, D. Anderson, M.R. Sawaya, M. Phillips, S. Sambashivan, J. Park, M. Landau, Q. Zhang, R. Clubb, F. Guo, T. Yeates, J. Nowick, J. Zheng, and M.J. Thompson for discussions, HHMI, NIH, NSF, the GATES foundation, and the Joint Center for Translational Medicine for support, R. Peterson for help with NMR experiments, E. Mandelkow for providing tau constructs, R. Riek for providing amyloid beta, J. Stroud for amyloid beta preparation. Support for JK was from the Damon Runyon Cancer Research Foundation, for HWC by the Ruth L. Kirschstein National Research Service Award, for JM from the programme for junior-professors by the ministry of science, Baden-Württemberg, and for SAS by a UCLA-IGERT bioinformatics traineeship

Track A Basic Science

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138319/1/jia218438.pd

Discovery and characterization of an endogenous CXCR4 antagonist.

12 p.-7 fig. Zirafi, O. et altCXCL12-CXCR4 signaling controls multiple physiological processes and its dysregulation is associated with cancers and inflammatory diseases. To discover as-yet-unknown endogenous ligands of CXCR4, we screened a blood-derived peptide library for inhibitors of CXCR4-tropic HIV-1 strains. This approach identified a 16 amino acid fragment of serum albumin as an effective and highly specific CXCR4 antagonist. The endogenous peptide, termed EPI-X4, is evolutionarily conserved and generated from the highly abundant albumin precursor by pH-regulated proteases. EPI-X4 forms an unusual lasso-like structure and antagonizes CXCL12-induced tumor cell migration, mobilizes stem cells, and suppresses inflammatory responses in mice. Furthermore, the peptide is abundant in the urine of patients with inflammatory kidney diseases and may serve as a biomarker. Our results identify EPI-X4 as a key regulator of CXCR4 signaling and introduce proteolysis of an abundant precursor protein as an alternative concept for chemokine receptor regulation.Peer reviewe

Direct visualization of HIV-enhancing endogenous amyloid fibrils in human semen

Naturally occurring fragments of the abundant semen proteins prostatic acid phosphatase (PAP) and semenogelins form amyloid fibrils in vitro. These fibrils boost HIV infection and may play a key role in the spread of the AIDS pandemic. However, the presen

Direct visualization of HIV-enhancing endogenous amyloid fibrils in human semen

Naturally occurring fragments of the abundant semen proteins prostatic acid phosphatase (PAP) and semenogelins form amyloid fibrils in vitro. These fibrils boost HIV infection and may play a key role in the spread of the AIDS pandemic. However, the presence of amyloid fibrils in semen remained to be demonstrated. Here, we use state of the art confocal and electron microscopy techniques for direct imaging of amyloid fibrils in human ejaculates. We detect amyloid aggregates in all semen samples and find that they partially consist of PAP fragments, interact with HIV particles and increase viral infectivity. Our results establish semen as a body fluid that naturally contains amyloid fibrils that are exploited by HIV to promote its sexual transmission

Liquefaction of Semen Generates and Later Degrades a Conserved Semenogelin Peptide That Enhances HIV Infection

Semen enhances HIV infection in vitro, but how long it retains this activity has not been carefully examined. Immediately postejaculation, semen exists as a semisolid coagulum, which then converts to a more liquid form in a process termed liquefaction. We demonstrate that early during liquefaction, semen exhibits maximal HIV-enhancing activity that gradually declines upon further incubation. The decline in HIV-enhancing activity parallels the degradation of peptide fragments derived from the semenogelins (SEMs), the major components of the coagulum that are cleaved in a site-specific and progressive manner upon initiation of liquefaction. Because amyloid fibrils generated from SEM fragments were recently demonstrated to enhance HIV infection, we set out to determine whether any of the liquefaction-generated SEM fragments associate with the presence of HIV-enhancing activity. We identify SEM1 from amino acids 86 to 107 [SEM1(86-107)] to be a short, cationic, amyloidogenic SEM peptide that is generated early in the process of liquefaction but that, conversely, is lost during prolonged liquefaction due to the activity of serine proteases. Synthetic SEM1(86-107) amyloids directly bind HIV-1 virions and are sufficient to enhance HIV infection of permissive cells. Furthermore, endogenous seminal levels of SEM1(86-107) correlate with donor-dependent variations in viral enhancement activity, and antibodies generated against SEM1(86-107) recognize endogenous amyloids in human semen. The amyloidogenic potential of SEM1(86-107) and its virus-enhancing properties are conserved among great apes, suggesting an evolutionarily conserved function. These studies identify SEM1(86-107) to be a key, HIV-enhancing amyloid species in human semen and underscore the dynamic nature of semen's HIV-enhancing activity. IMPORTANCE Semen, the most common vehicle for HIV transmission, enhances HIV infection in vitro, but how long it retains this activity has not been investigated. Semen naturally undergoes physiological changes over time, whereby it converts from a gel-like consistency to a more liquid form. This process, termed liquefaction, is characterized at the molecular level by site-specific and progressive cleavage of SEMs, the major components of the coagulum, by seminal proteases. We demonstrate that the HIV-enhancing activity of semen gradually decreases over the course of extended liquefaction and identify a naturally occurring semenogelin-derived fragment, SEM1(86-107), whose levels correlate with virus-enhancing activity over the course of liquefaction. SEM1(86-107) amyloids are naturally present in semen, and synthetic SEM1(86-107) fibrils bind virions and are sufficient to enhance HIV infection. Therefore, by characterizing dynamic changes in the HIV-enhancing activity of semen during extended liquefaction, we identified SEM1(86-107) to be a key virus-enhancing component of human semen

Discovery and Characterization of an Endogenous CXCR4 Antagonist

CXCL12-CXCR4 signaling controls multiple physiological processes and its dysregulation is associated with cancers and inflammatory diseases. To discover as-yet-unknown endogenous ligands of CXCR4, we screened a blood-derived peptide library for inhibitors of CXCR4-tropic HIV-1 strains. This approach identified a 16 amino acid fragment of serum albumin as an effective and highly specific CXCR4 antagonist. The endogenous peptide, termed EPI-X4, is evolutionarily conserved and generated from the highly abundant albumin precursor by pH-regulated proteases. EPI-X4 forms an unusual lasso-like structure and antagonizes CXCL12-induced tumor cell migration, mobilizes stem cells, and suppresses inflammatory responses in mice. Furthermore, the peptide is abundant in the urine of patients with inflammatory kidney diseases and may serve as a biomarker. Our results identify EPI-X4 as a key regulator of CXCR4 signaling and introduce proteolysis of an abundant precursor protein as an alternative concept for chemokine receptor regulation