Mabinlin

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Mabinlin 1
Identifiers
Symbol 2SS1_CAPMA
UniProt P80351
Mabinlin 2
File:Mabinlin II 2DS2.png
Also known as: Mabinlin II, MAB II
Identifiers
Symbol 2SS2_CAPMA
PDB 2DS2
UniProt P30233
Mabinlin 3
Identifiers
Symbol 2SS3_CAPMA
UniProt P80352
Mabinlin 4
Identifiers
Symbol 2SS4_CAPMA
UniProt P80353

Mabinlins are sweet-tasting proteins extracted from the seed of Mabinlang (Capparis masaikai Levl.), a Chinese plant growing in Yunnan province. There are four homologues. Mabinlin-2 was first isolated in 1983[1] and characterised in 1993,[2] and is the most extensively studied of the four. The other variants of mabinlin-1, -3 and -4 were discovered and characterised in 1994.[3]

Protein structures

The 4 mabinlins are very similar in their amino acids sequences (see below).

Chain A
M-1: EPLCRRQFQQ HQHLRACQRY IRRRAQRGGL VD
M-2: QLWRCQRQFL QHQRLRACQR FIHRRAQFGG QPD
M-3: EPLCRRQFQQ HQHLRACQRY LRRRAQRGGL AD
M-4: EPLCRRQFQQ HQHLRACQRY LRRRAQRG

Chain B
M-1: EQRGPALRLC CNQLRQVNKP CVCPVLRQAA HQQLYQGQIE GPRQVRQLFR AARNLPNICK IPAVGRCQFT RW
M-2: QPRRPALRQC CNQLRQVDRP CVCPVLRQAA QQVLQRQIIQ GPQQLRRLFD AARNLPNICN IPNIGACPFR AW
M-3: EQRGPALRLC CNQLRQVNKP CVCPVLRQAA HQQLYQGQIE GPRQVRRLFR AARNLPNICK IPAVGRCQFT RW
M-4: EQRGPALRLC CNQLRQVNKP CVCPVLRQAA HQQLYQGQIE GPRQVRRLFR AARNLPNICK IPAVGRCQFT RW
Amino acid sequence of Mabinlins homologues are adapted from Swiss-Prot biological database of protein.[4][5][6][7]

The molecular weights of Mabinlin-1, Mabinlin-3 and Mabinlin-4 are 12.3 kDa, 12.3 kDa and 11.9 kDa, respectively.[3]

With a molecular weight of 10.4kDa, mabinlin-2 is lighter than mabinlin-1. It is a heterodimer consisting of two different chains A and B. The A chain is composed of 33 amino acid residues and the B chain is composed of 72 amino acid residues. The B chain contains two intramolecular disulfide bonds and is connected to the A chain through two intermolecular disulfide bridges.[2][8]

Mabinlin-2 is the sweet-tasting protein with the highest known thermostability,[9] which is due to the presence of the four disulfide bridges.[10] It has been suggested also that the difference in the heat stability of the different mabinlin homologues is due to the presence of an arginine residue (heat-stable homologue) or a glutamine (heat-unstable homologue) at position 47 in the B-chain.[3]

Sweetness properties

Mabinlins sweetness were estimated to be about 100-400 times that of sucrose on molar basis, 10 times sucrose on a weight basis,[2][3] which make them less sweet than thaumatin (3000 times) but elicit a similar sweetness profile.[11]

The sweetness of mabinlin-2 is unchanged after 48 hours incubation at 80°C.[2]

Mabinlin-3 and -4 sweetness stayed unchanged after 1 hour at 80°C, while mabinlin-1 loses sweetness after 1 hour at the same condition.[3][12]

As a sweetener

Mabinlins, as proteins, are readily soluble in water and found to be highly sweet, however mabinlin-2 with its high heat stability has the best chance to be used as a sweetener.

During the past decade, attempts have been made to produce mabinlin-2 industrially. The sweet-tasting protein has been successfully synthesised by a stepwise solid-phase method in 1998, however the synthetic protein had an astringent-sweet taste.[8]

Mabinlin-2 has been expressed in transgenic potato tubers, but no explicit results have been reported yet.[13] However, patents to protect production of recombinant mabinlin by cloning and DNA sequencing have been issued.[14]

References

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See also