Claire Lupton

Lengsin protein structure varies depending on the species in which it is presented due to the varying genetics within species. For example, in humans the n-terminal domain is the biggest indication that Lengsin contributes to the formation of the eye via evolution. This polymer consists of 421 residues composed of primarily <scene name='83/837873/Structural_composition/3'>alpha helix residues (140 residues) and 79 Beta Sheets</scene>. It is approximately 17  Angstroms in length and has a D₆ Dihedral globular symmetry.<ref name=ref5>PMID:RCSB Protein Data Bank. (n.d.). PBD Structure. Retrieved from http://www.rcsb.org/pdb/explore/remediatedSequence.do;jsessionid=CD7F39FC7BF568D64508042AF64E04A0?structureId=2J9I¶</ref> A D₆ symmetry constitutes 6 points of rotation and reflection across the Dihedral symmetry axis. It also has twelve Glutamate-ammonia ligase proteins. <scene name='83/837873/Hydrophobic_areas_of_lengsin/1'>Lengsin is generally neither highly hydrophobic, nor highly hydrophilic</scene>. Although, it does have certain hydrophobic binding sites used for interaction with other hydrophobic molecules during lens formation. In total, there are six binding sites on lengsin which contribute to lens formation.<ref name=ref1>PMID:Grassi , F. J., Moretto, N. J., Rivetti, C. J., Cellai, S. J., Betti, M. J., Márquez , A. Ontonello, S. J. (2006). Structural and Functional Properties of Lengsin, a Pseduo-Glutamine Synthetase in the Transparent Human Lens . Retrieved from https://maryville.illiad.oclc.org/illiad/pdf/173917.pdf</ref> These proteins are found in a several vertebrate species, including prokaryotes, but they are most abundant in vertebrates.  

Lengsin’s overall role is to help participates in the formation of the lens during the cellular development of vertebrates. However, its discovery is a relatively recent addition to modern science, so researchers have not found the exact mechanism of this protein. Although, there is some general knowledge of the overall functions and mechanisms of this protein, there are only guesses as to what the specific cellular contributions could be. Since lengsin is classified as a Glutamine Synthetase, it fixes ammonia. There are several proposed functions of lengsin’s nitrogen fixation, however. With this, conversely, lies a predicament. The missing link in this proposal is that vertebrate eyes contain another sub type of Glutamine Synthetases within the urea cycle that fixates ammonia prior to lengsin. So, the prospective thought process behind this mechanism is the tissue is inefficient at fixing the ammonia within the urea cycle, and needs aid via lengsin. To support this hypothesis, tissues contained in the eye are classified as avascular tissues. Since the lens is avascular, this could theoretically disrupt the urea cycle. Thus, lengsin would need to be present to complete the nitrogen fixation.  In fact, crystalline structures help to prove this. It is thought that the deamination requires an enzyme with an asparagine and glutamine side chains to assist deamination. A different suggestion that was made was that the function of lengsin was to chaperone the formation of the lens.The overall structure of Lengsin in humans is wildly similar to other crystalline chaperone proteins.  <ref name=ref2>PMID:Wyatt, K., White, H. E., Wang, L., Bateman, O. A., Slingsby, C., Orlova, E. V., & Wistow, G. (2006). Lengsin is a survivor of an ancient family of class I glutamine synthetases re-engineered by evolution for a role in the vertebrate lens. Structure (London, England : 1993), 14(12), 1823–1834. https://doi.org/10.1016/j.str.2006.10.008</ref> Finally, Lengsin is capable of being deactivated by the <scene name='83/837873/Amyloid_beta_protein/1'>amyloid-Beta protein</scene> which is, interestingly enough, a well known binding protein associated with Alzheimer's disease.<ref name=ref1>PMID:Grassi , F. J., Moretto, N. J., Rivetti, C. J., Cellai, S. J., Betti, M. J., Márquez , A. Ontonello, S. J. (2006). Structural and Functional Properties of Lengsin, a Pseduo-Glutamine Synthetase in the Transparent Human Lens . Retrieved from https://maryville.illiad.oclc.org/illiad/pdf/173917.pdf</ref>

Unlike zebrafish, adult humans appear to have high levels of lengsin in the eye.In fact, it is one of the most abundant, non-crystallized proteins present in the human lens. However, one exception does apply: cataracts. If cataracts are present, lengsin levels are low <ref name=ref1>PMID:Wyatt, K., White, H. E., Wang, L., Bateman, O. A., Slingsby, C., Orlova, E. V., & Wistow, G. (2006). Lengsin is a survivor of an ancient family of class I glutamine synthetases re-engineered by evolution for a role in the vertebrate lens. Structure (London, England : 1993), 14(12), 1823–1834. https://doi.org/10.1016/j.str.2006.10.008</ref>. Therefore, it is believed that this protein is crucial in not only lens formation, but maintaining stability and transparency of the human eye as well. Furthermore, this could be why elderly patients are most prone to cataracts, due to the maturation of the eye causing loss of lengsin, which results in a less structurally desired lens.

In homo sapiens, the genetic code for this protein is found on chromosome 6.  

While this is different from zebrafish, another contrast between the two species of lengsin is the presence in the body. While zebrafish were found to have lengsin specifically in the eyes, humans have some small amounts of lengsin in other tissues as well (under specific circumstances) .<ref name=ref1>PMID:Wyatt, K., White, H. E., Wang, L., Bateman, O. A., Slingsby, C., Orlova, E. V., & Wistow, G. (2006). Lengsin is a survivor of an ancient family of class I glutamine synthetases re-engineered by evolution for a role in the vertebrate lens. Structure (London, England : 1993), 14(12), 1823–1834. https://doi.org/10.1016/j.str.2006.10.008</ref> Thus, this protein is a multipurpose protein present in humans.