Elucidation of African elephant beta casein phosphorylation state and casein micelle structure
| dc.contributor.advisor | Osthoff, G. | |
| dc.contributor.advisor | Kemp, G. | |
| dc.contributor.author | Madende, Moses | |
| dc.date.accessioned | 2017-07-25T07:01:13Z | |
| dc.date.available | 2017-07-25T07:01:13Z | |
| dc.date.issued | 2017-01 | |
| dc.description.abstract | English: The exact structure of casein micelles still remains a debated subject. While most of the experimental work on cow caseins and casein micelles has provided a wealth of data, data of caseins and casein micelles of non-bovine origin provide a new insight into the structure of casein micelles. Microscopic examination of cow, sheep, horse, human and African elephant milk casein micelles show that the respective casein micelles are all spherical in shape but differ in size as well as surface appearances. Human casein micelles were the largest of the casein micelles whereas sheep casein micelles were the smallest. Apart from their smaller size, sheep micelles also had a smooth surface compared to a rough surface observed on the rest of the casein micelles. African elephant casein micelles were the second largest of the five casein micelles compared. It may be derived that, although casein micelle shape and size seem to be species specific, the differences observed may be a result of the differences in total casein content, the proportions of the individual casein types and the presence and or absence of some of the casein types. The elucidation of African elephant β-casein phosphorylation state by LC MS/MS, showed the presence of a single phosphorylation site at Ser9. In contrast, electrophoresis analysis showed that there are up to five phosphoforms of African elephant β-casein. The LC MS/MS also showed that the presence of a short length African elephant β-casein that is 200 amino acids long and that the gene sequences coded for by exons 4 and 5 have been truncated. Homology modeling of cow, sheep, horse, human and African elephant caseins showed that the secondary structure of α-caseins predominantly consist of α-helices, whereas the secondary structure of β- and κ-caseins is dominated by random coils. Alpha caseins give micelles a slightly compact structure whereas random coils result in a more open and larger size of micelles. These structural differences of caseins could possibly explain the varied size of casein micelles in milk. Comparative genomics of casein genes across mammalian species shows that several mammalian species are devoid of CNS1S1 and CSN1S2 genes. Considering the evolution of the casein gene locus organization, it appears that the CNS1S1 gene has been lost whereas the CSN1S2 gene has not been gained or developed in these species. In contrast, the CSN2 and CSN3 genes have been preserved and gained respectively, in most mammalian species. This suggests that these genes have a more important role in casein micelle formation and consequently the sequestration of large amounts of calcium and phosphate. Evidence from this study suggests that studying of non-cow caseins may shed more light on the casein micelle structure. | en_ZA |
| dc.description.abstract | Afrikaans: Die presiese struktuur van kaseïenmiselle bly 'n debateerbare onderwerp. Terwyl die meeste eksperimentele werk op bees kaseïene en kaseïenmiselle 'n magdom data gelewer het, dra data van kaseïene en kaseïenmiselle van nie-bees oorsprong by tot insig in die stuktuur van kaseïenmiselle. Mikroskopiese ondersoeke van kaseïenmiselle van bees, skaap, perd, mens en Afrikaanse olifant wys dat die onderskeie kaseïenmiselle almal sferies in vorm is, maar verskil in grootte en oppervlakvoorkoms. Menslike kaseïenmiselle was die grootste, terwyl dié van skaap die kleinste was. Buiten die kleiner grootte, het skaapkaseïenmiselle 'n gladde oppervlak vergeleke met die growwe oppervlak van die ander. Kaseïenmiselle van Afrikaanse olifant was die tweede grootste van die vyf bestudeerdes. Daar kan afgelei word dat, alhoewel die vorm en grootte van kaseïenmiselle spesiespesifiek voorkom, die waargenome verskille ook die resultaat mag wees van verskille in totale kaseïeninhoud en/of die afwesigheid van sekere kaseïentipes. Die opklaring van Afrikaanse olifant β-kaseïen fosforileringstatus deur LC MS/MS, het die teenwoordigheid van 'n enkele fosforileringspunt by Ser9 aangedui. In kontras het elektroforetiese analise voorgetsel dat to vyf fosfo-forme van die afrikaanse olifant β-kaseïen mag voorkom. Die LC MS/MS het ook gewys dat die Afrikaanse olifant β-kaseïen 200 aminosure lank is en dat die geengebiede wat deur eksons 4 en 5 kodeer word, verkort is. Homologie modelering van bees, skaap, perd en Afrikaanse olifant kaseïene dui daarop dat die sekondêre struktuur van α-kaseïene hoofsaaklik bestaan uit α-helikse, terwyl die sekondêre struktuur van β- en κ-kaseïene gedomineer word deur willekeurige struktuur. Alfa kaseïene gee aan miselle 'n gedeeltelik stewige struktuur, terwyl willekeurige struktuur lei tot 'n oop struktuur en groter miselle. Hierdie strukturele verskille mag moontlik die variasie in kaseïenmiselgroottes in melk verklaar. Vergelykende genomika van kaseïengene oor soogdierspesies heen wys dat sekere soogdiespesies nie die CNS1S1 en CSN1S2 gene besit nie. Wanneer die ewolusie van die rangskikking van die kaseïengeenlokusse in ag geneem word, kom dit voor asof die CNS1S1 geen verlore geraak het, terwyl die CSN1S2 geen nie in hierdie spesies ontwikkel het nie. Daarteenoor was die CNS2 en CSN3 gene beskerm of verwerf in die meeste soogdierspesies. Dit stel voor dat hierdie gene 'n belangriker rol speel in die vorming van kaseïnmiselle en gevolglike sekwestrasie van groot hoeveelhede kalsium en fosfaat. Bewyse uit hierdie studie stel voor dat die bestudering van nie-koei kaseïene meer lig mag werp op die struktuurkennis van kaseïenmiselle. | af |
| dc.description.sponsorship | National Research Foundation (NRF) | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/11660/6508 | |
| dc.language.iso | en | en_ZA |
| dc.publisher | University of the Free State | en_ZA |
| dc.rights.holder | University of the Free State | en_ZA |
| dc.subject | African elephant | en_ZA |
| dc.subject | Casein micelle | en_ZA |
| dc.subject | Phosphorylation | en_ZA |
| dc.subject | Mass spectrometry | en_ZA |
| dc.subject | Comparative genomics | en_ZA |
| dc.subject | Structure modeling | en_ZA |
| dc.subject | Casein | en_ZA |
| dc.subject | Milk proteins | en_ZA |
| dc.subject | Thesis (Ph.D. (Microbial, Biochemical and Food Biotechnology))--University of the Free State, 2017 | en_ZA |
| dc.title | Elucidation of African elephant beta casein phosphorylation state and casein micelle structure | en_ZA |
| dc.type | Thesis | en_ZA |