Welcome to the Utopia Forums! Register a new account
The current time is Thu Nov 14 12:38:54 PST 2019

Utopia Talk / Politics / Cockroach Milk, Superfood for Space Age
Forwyn
Member
Tue Oct 22 10:33:25
1. Introduction
Viviparity, the maternal nourishment of embryos during development, is a highly evolved type of reproduction that occurs in many groups of animals. Cockroaches have evolved over the past 320 million years (Garwood & Sutton, 2010[Garwood, R. & Sutton, M. (2010). Biol. Lett. 6, 699-702.]; Garwood et al., 2012[Garwood, R., Ross, A., Sotty, D., Chabard, D., Charbonnier, S., Sutton, M. & Withers, P. J. (2012). PLoS One, 7, e45779.]). An interesting feature of their evolution lies in their mode of reproduction. There are three general types of cockroaches: oviparous, ovoviviparous and viviparous (Roth, 1970[Roth, L. M. (1970). Annu. Rev. Entomol. 15, 75-96.]). The oviparous species (e.g. Periplaneta ameri­cana) either deposit the ootheca (enclosing the fertilized eggs) onto a substrate or retain them, extruded and attached to the female's body (Roth & Willis, 1954[Roth, L. M. & Willis, E. R. (1954). Smiths. Misc. Collect. 122, 1-49.]). The ovoviviparous species (e.g. Rhyparobia maderae) deposit the ootheca in the brood sac of the female. In this brood sac or uterus, the embryos are provided with protection and water, but not with nutrients (Nalepa & Bell, 1997[Nalepa, C. A. & Bell, W. J. (1997). The Evolution of Social Behavior in Insects and Arachnids. Cambridge University Press.]). Diploptera punctata is the only known viviparous cockroach, an evolutionarily advanced condition in which the eggs have little yolk, but the developing offspring are nourished directly by the mother from the brood sac wall. Viviparity enhances larval development, because the time to reproductive maturity is substantially reduced in D. punctata relative to ovoviviparous species (Roth & Willis, 1954[Roth, L. M. & Willis, E. R. (1954). Smiths. Misc. Collect. 122, 1-49.]; Willis et al., 1958[Willis, E. R., Riser, G. R. & Roth, L. M. (1958). Ann. Entomol. Soc. Am. 51, 53-69.]; Stay & Coop, 1973[Stay, B. & Coop, A. (1973). J. Insect Physiol. 19, 147-171.], 1974[Stay, B. & Coop, A. C. (1974). Tissue Cell, 6, 669-693.]; Roth, 1989[Roth, L. M. (1989). Proc. Entomol. Soc. Wash. 91, 441-451.]). Utilizing the sparse yolk, D. punctata embryos quickly develop strong pharyngeal muscles and a simple gut, enabling them to imbibe and deposit in their midguts a protein-rich liquid milk secreted by the brood sac (Stay & Coop, 1973[Stay, B. & Coop, A. (1973). J. Insect Physiol. 19, 147-171.], 1974[Stay, B. & Coop, A. C. (1974). Tissue Cell, 6, 669-693.]; Evans & Stay, 1989[Evans, L. D. & Stay, B. (1989). Invertebr. Reprod. Dev. 15, 171-176.]). This milk provides a 60-fold whole-body increase in protein during embryonic development (Stay & Coop, 1973[Stay, B. & Coop, A. (1973). J. Insect Physiol. 19, 147-171.]). Complementary DNA analyses revealed 22 distinct but similar peptides encoded by milk genes with homology to the lipocalin family of lipid-binding proteins (Williford et al., 2004[Williford, A., Stay, B. & Bhattacharya, D. (2004). Evol. Dev. 6, 67-77.]), which are referred to as lipocalin-like milk proteins or Lili-Mip in this article. Soon after ingestion of the liquid milk, protein crystals develop within the embryo midgut (Ingram et al., 1977[Ingram, M. J., Stay, B. & Cain, G. D. (1977). Insect Biochem. 7, 257-267.]). The crystals were shown to contain milk glycoproteins, although less glycosylated than at the time of secretion from the brood sac (Ingram et al., 1977[Ingram, M. J., Stay, B. & Cain, G. D. (1977). Insect Biochem. 7, 257-267.]; Williford et al., 2004[Williford, A., Stay, B. & Bhattacharya, D. (2004). Evol. Dev. 6, 67-77.]). Thus, viviparity in D. punctata involves the evolution of a milk-secreting brood sac and rapid development of embryos that are able to drink and, importantly, store complete nutrients (protein, carbohydrate and lipid) concentrated in crystalline form. The properties of these in vivo-grown milk protein crystals are associated with the evolution of viviparity in cockroaches and are the subject of the current study.

In vivo-grown protein crystals have been identified from a diverse group of organisms (Doye & Poon, 2006[Doye, J. P. K. & Poon, W. C. K. (2006). Curr. Opin. Colloid Interface Sci. 11, 40-46.]; Lange et al., 1982[Lange, R. H., Grodziński, Z. & Kilarski, W. (1982). Cell Tissue Res. 222, 159-165.]; Dogan et al., 2012[Dogan, S., Barnes, L. & Cruz-Vetrano, W. P. (2012). Head Neck Pathol. 6, 111-120.]; Pande et al., 2001[Pande, A., Pande, J., Asherie, N., Lomakin, A., Ogun, O., King, J. & Benedek, G. B. (2001). Proc. Natl Acad. Sci. USA, 98, 6116-6120.]). Their presence inside cells has been linked to biological functions such as insulin secretion (Dodson & Steiner, 1998[Dodson, G. & Steiner, D. (1998). Curr. Opin. Struct. Biol. 8, 189-194.]), sorting of secretory proteins in the Golgi apparatus (Arvan & Castle, 1998[Arvan, P. & Castle, D. (1998). Biochem. J. 332, 593-610.]), pathogenicity in Bacillus thuringiensis (van Frankenhuyzen, 2013[Frankenhuyzen, K. van (2013). J. Invertebr. Pathol. 114, 76-85.]), storage mechanisms for infectious viruses (Coulibaly et al., 2005[Coulibaly, F., Chevalier, C., Gutsche, I., Pous, J., Navaza, J., Bressanelli, S., Delmas, B. & Rey, F. A. (2005). Cell, 120, 761-772.], 2007[Coulibaly, F., Chiu, E., Ikeda, K., Gutmann, S., Haebel, P. W., Schulze-Briese, C., Mori, H. & Metcalf, P. (2007). Nature (London), 446, 97-101.], 2009[Coulibaly, F., Chiu, E., Gutmann, S., Rajendran, C., Haebel, P. W., Ikeda, K., Mori, H., Ward, V. K., Schulze-Briese, C. & Metcalf, P. (2009). Proc. Natl Acad. Sci. USA, 106, 22205-22210.]) and for developmental proteins in seeds (Doye & Poon, 2006[Doye, J. P. K. & Poon, W. C. K. (2006). Curr. Opin. Colloid Interface Sci. 11, 40-46.]) and eggs (Papassideri et al., 2007[Papassideri, I. S., Trougakos, I. P., Leonard, K. R. & Margaritis, L. H. (2007). J. Insect Physiol. 53, 370-376.]; Snigirevskaya et al., 1997[Snigirevskaya, E. S., Hays, A. R. & Raikhel, A. S. (1997). Cell Tissue Res. 290, 129-142.]; Lange et al., 1982[Lange, R. H., Grodziński, Z. & Kilarski, W. (1982). Cell Tissue Res. 222, 159-165.]). In humans, naturally occurring crystals have been associated with disease conditions including histiocytosis (Dogan et al., 2012[Dogan, S., Barnes, L. & Cruz-Vetrano, W. P. (2012). Head Neck Pathol. 6, 111-120.]), hemoglobin C (Doye & Poon, 2006[Doye, J. P. K. & Poon, W. C. K. (2006). Curr. Opin. Colloid Interface Sci. 11, 40-46.]) and cataracts (Pande et al., 2001[Pande, A., Pande, J., Asherie, N., Lomakin, A., Ogun, O., King, J. & Benedek, G. B. (2001). Proc. Natl Acad. Sci. USA, 98, 6116-6120.]). In these conditions crystal growth might be coincidental, but is associated with pathology. In this report, our analysis of Lili-Mip crystals shows that they contain a heterogeneous mixture of amino-acid sequences in vivo and diffract to atomic resolution.

Macromolecular crystals for X-ray diffraction studies are typically grown from pure and homogeneous samples. Heterogeneity from post-translational modifications is considered to significantly reduce the probability of obtaining well diffracting crystals. In the case of glycosylation, which is heterogeneous by nature, great efforts are made to deglycosylate proteins of interest to favour chemically homogeneous and structurally monodisperse molecules prior to crystallization. Anecdotally, chemists and early biochemists used crystallization to isolate single-molecular species.

The number of X-ray crystal structures that have been determined from in vivo-grown crystals is low. The major challenge in their structure determination lies in the handling of such crystals at third-generation X-ray sources owing to their small physical dimensions (Koopmann et al., 2012[Koopmann, R. et al. (2012). Nat. Methods, 9, 259-262.]). Crystal structures of baculovirus polyhedra have been determined up to 2.2 Å resolution from microcrystals grown in vivo (Coulibaly et al., 2009[Coulibaly, F., Chiu, E., Gutmann, S., Rajendran, C., Haebel, P. W., Ikeda, K., Mori, H., Ward, V. K., Schulze-Briese, C. & Metcalf, P. (2009). Proc. Natl Acad. Sci. USA, 106, 22205-22210.]). Baculovirus expression systems have been utilized to induce intracellular crystallization of cathepsin B from Trypanosoma brucei (TbCatB) and Cytoplasmic polyhedrosis virus (CPV) polyhedra from Bombyx mori, thereby allowing structure determination of TbCatB to 2.1 Å resolution (Redecke et al., 2013[Redecke, L. et al. (2013). Science, 339, 227-230.]; Koopmann et al., 2012[Koopmann, R. et al. (2012). Nat. Methods, 9, 259-262.]) and of CPV to 2.0 Å resolution (Coulibaly et al., 2007[Coulibaly, F., Chiu, E., Ikeda, K., Gutmann, S., Haebel, P. W., Schulze-Briese, C., Mori, H. & Metcalf, P. (2007). Nature (London), 446, 97-101.]). In vivo-grown crystals have also recently been interrogated by serial femtosecond crystallography (SFX) at X-ray free-electron laser (XFEL) sources as a potential solution for solving structures of systems that are not amenable to conventional crystallo­graphy, such as macromolecular complexes and chemically untreated proteins (Gallat et al., 2014[Gallat, F.-X. et al. (2014). Philos. Trans. R. Soc. B Biol. Sci. 369, 20130497.]). The structure of Bacillus thuringiensis Cry3A toxin from in vivo-grown crystals has been determined directly from the bacterial cells using SFX (Sawaya et al., 2014[Sawaya, M. R. et al. (2014). Proc. Natl Acad. Sci. USA, 111, 12769-12774.]). With the exception of CPV, none of these proteins crystallized within their functional niche.

All of the crystals described above could be called in cellulo crystals. In comparison to in cellulo-grown crystals, relatively large protein crystals (up to 10 × 10 × 30 µm) were identified in the midgut (in vivo) of developing embryos of the cockroach D. punctata (Fig. 1[link]; Ingram et al., 1977[Ingram, M. J., Stay, B. & Cain, G. D. (1977). Insect Biochem. 7, 257-267.]). While the cytoplasmic volumes of cells impose size constraints on protein crystals grown in cellulo, the substantially larger volume of the cockroach midgut allows larger crystals to develop. Surprisingly, these protein crystals diffracted to 1.2 Å resolution and we report the first structure of a naturally occurring and chemically unaltered, heterogeneous protein crystal grown in vivo at atomic resolution.

http://journals.iucr.org/m/issues/2016/04/00/jt5013/
show deleted posts

Your Name:
Your Password:
Your Message:
Bookmark and Share