Characterisation of mabinlin-like sweet protein, the 2s albumin seed storage protein from Theobroma cacao

Norzulaiha Abd. Karim (2020) Characterisation of mabinlin-like sweet protein, the 2s albumin seed storage protein from Theobroma cacao. Masters thesis, Universiti Malaysia Sabah.

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Abstract

The proteomic study revealed that a mabinlin-like protein with a 32.2% sequence identity, further identified as 2S albumin seed storage protein (Tc-2S precursor) expressed in Theobroma cacao. Suggesting that the Tc-2S precursor might serve as an alternative source for heat stable mabinlin II. Interestingly, the Tc-2S precursor reported to undergo self-maturation yielding a mature region consists of a heavychain subunit (Tc-9M) and a light-chain subunit (Tc-4M) which are linked by disulfide bonds. The Tc-9M corresponds to the B-chain subunit of mabinlin II, which the main structural element for the sweetness properties. Indeed, the N-terminal segment of Tc-9M (Nt-9M) was a region that resembles mabinlin II. It is therefore assumed that Tc-9M or Nt-9M proteins might specifically bind to human sweet taste receptors, hT1R2-T1R3 receptor and exhibit sweet taste. However, the sweetness properties of these proteins remain to be confirmed. In addition, there is no doubt that 2S albumin from many plants was reported to be involved in plant defensive mechanisms through its antibacterial, antifungal, and other biological activities. This study aims to characterize the sweetness properties of recombinant Tc-9M and Nt-9M proteins, and their role in plant defense mechanisms through their antibacterial, antifungal, and antitryptic activities. For this purpose, the optimized Tc-2S precursor, Tc-9M, and Nt- 9M genes were chemically synthesized, ligated into pET-32a( +) plasmid, and expressed under E coli BL21(DE3) system. The overexpression results showed that the Tc-2S precursor unable to express either as soluble or insoluble protein under the E coli system. Meanwhile other variants, the Tc-9M and Nt-9M protein were successfully expressed as soluble proteins and further purified with a yield of 32. 73 mg and 23.74 mg from 300 ml culture, respectively. The 3D-docking computational analysis showed that Tc-9M and Nt-9M proteins bound to the hT1R2-T1R3 receptor, yet theoretically displayed weaker affinity than the Tc-2S precursor and other sweet proteins did. Besides, the panel test showed that the purified recombinant Tc-9M and Nt-9M proteins did not exhibit any sweet response at the concentration up to 32.5 μM. The weak affinity of Tc-9M and Nt-9M to the receptors might account for the absence of sweetness response. The Tc-9M protein displayed remarkable inhibition property towards Salmonella sp., Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Bacillus cereusin a concentration dependent manner. In addition, Tc-9M protein was also able to inhibit the growth of Saccharomyces cerevisiae and Pichia pastoris, but did not display antifungal activity against Trichoderma asperellum. The inhibition properties of Tc-9M protein might be related to the physiological roles of this protein in the defense mechanism of T. cocoa. By contrast, the Nt-9M protein only having antibacterial activity against Salmonella sp. and 5. aureus., which suggested that the whole region of this protein is required for generating complete inhibition properties. Meanwhile, instead of antitryptic activity, both Tc-9M and Nt-9M proteins exhibited proteolytic activity. Altogether, it is obvious that sequence similarity does not necessarily correlate to the sweetness properties. Besides, the result also suggested that a single chain of Tc-2S was sufficient for antibacterial and antifungal activities of this protein.

Item Type:	Thesis (Masters)
Keyword:	c-2S precursor, Mabinlin-like protein, Sweetness properties, 2S albumin, Theobroma cacao
Subjects:	Q Science > QP Physiology > QP1-(981) Physiology > QP501-801 Animal biochemistry
Department:	INSTITUTE > Biotechnology Research Institute (BRI)
Depositing User:	DG MASNIAH AHMAD -
Date Deposited:	17 Jan 2025 14:19
Last Modified:	17 Jan 2025 14:19
URI:	https://eprints.ums.edu.my/id/eprint/42620

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