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Crystals of L-aspartic acid are monoclinic (P21) with a=7.617, b= 6.982, c= 5.142/~, ,8=99.84 °, Z=2. The crystals are often more or less twinned. The structure was solved in the hOl projection by the Patterson vector shift method. The structure was refined with 602 diffractometer hkl data to a final R value of 0.04. The molecules are in the zwitterionic form. A rigid three-dimensional network of intermolecular 'hydrogen bonds' is found.

Thaumatin and monellin are the two sweetest compounds known to man-about 100,000 times sweeter than sugar on a molar basis and 3000 times on a weight basis. These proteins represent a unique class of proteins that are tasteactive. We report the three-dimensional structure of thaumatin I at 3.1 A resolution.Taste is one of the least understood senses from a biochemical point of view. Sweet taste can be elicited to varying degrees by a wide variety of compounds in high concentration, such as mono-and disaccharides, several amino acids, dipeptide derivatives, glycerol, cyclamates, saccharine, acesulfame, some hydrated inorganic compounds, and others.Sensations of sweet taste are elicited by sweet compounds binding to sweet receptors of taste buds on the tongue, similar to hormone-hormone receptor binding. However, the similarity ends here. A 50% binding of hormone receptors usually occurs at around 10-8 to 10-11 M concentration of hormones, but in the case of sweet receptors the concentration to register sweet taste is about 10-1 to 10-3 M of sucrose. Furthermore, like other sensory perceptions, taste is associated with a unique set of sensation parameters. These are threshold concentration, onset time, intensity, saturation concentration, lingering time, aftertaste, and potentiation of other tastes or flavors. Systematic studies of these properties of taste-active compounds have been difficult in the past because of high levels of nonspecific binding between the sweet comnpounds and the sweet receptors due to the high concentrations of the sweet compounds required to elicit the sweet taste.One of the most interesting and unusual recent findings is the existence of two intensely sweet proteins, monellin and thaumatin (for a recent review, see ref. 1). The sweet taste of the proteins can be registered at a very low concentration (10' M), comparable to those in hormone-hormone receptor interaction. These proteins are about 100,000 times sweeter than sucrose on a molar basis and several thousand times sweeter on a weight basis. In fact, these two proteins are the two sweetest compounds known to man. With these proteins, studies similar to those performed for hormonehormone receptors can be initiated. Three-dimensional structures of these proteins are likely to provide a solid foundation upon which studies to understand the molecular basis of sweet taste can be designed. We here report the crystal structure of thaumatin I at 3.1 A resolution.Thaumatins have been isolated from the fruit of a West African rain forest shrub, Thaumatococcus daniellii Benth (2), which has been used for centuries by inhabitants of the region to sweeten foods such as bread and palm wine, There are two major sweet proteins in the fruit, thaumatin I and II, with almost identical molecular weights of 22,000. They consist of 207 amino acids and have identical amino acid sequences except for five residues (3, 4). There are no histidine residues, but there are eight disulfide bonds. Partially pure thaumatin is available commercially from Si...

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