## 3 Results and Discussion
### Rattus Norvegicus and Homo sapiens mGluR1s Shared Homology  
The aim of this work was to estimate the interactions between mGluR1 and umami dipeptides found in dry-cured ham. These findings, in joint with peptidomic and further sensory analysis, will provide interesting evidence about the development of dry-cured ham flavor by the generation of short peptides, and will contribute to predict the taste of unknown peptides present in foods. As the _Homo sapiens_ mGluR1 crystal structure (PDB ID: 3K59; UniProt ID: Q13255) was recently resolved, and there is little information about its mechanism, a first comparative study with the most frequently employed _Rattus norvegicus_ mGluR1 (PDB ID: 1 EWK; UniProt ID: P23385) was conducted. Figure 1 indicates an alignment [57] of both FASTA sequences. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Dipeptide a ** & **Net Charge** & **Hydrophobicity** & **Steric** & **Main Residue Attribute** \\  & **Parental Protein b ** & **(Value (p)) c ** & **Hindrance d ** & **Main Residue Attribute** \\  & & Unknown & 0.1 (7.88) & \(-\)0.08 & 0.26 & aliphatic, basic \\  & & MLC1 & \(-\)1 (0.69) & -0.23 & 0.64 & acidic, aliphatic \\  & & DG & & & & \\  & Unknown & \(-\)1 (0.68) & \(-\)0.28 & 0.72 & acidic, aliphatic \\  & & TTN & & & & \\  & [55] & \(-\)2 (0.85) & \(-\)0.62 & 0.68 & acidic, acidic \\  & [54] & & & & & \\  & Unknown & \(-\)1 (1.01) & \(-\)0.44 & 0.60 & acidic, polar \\  & & & & & \\  & Unknown & \(-\)1 (0.94) & \(-\)0.04 & 0.69 & acidic, aliphatic \\  & & & & & \\  & Unknown & 0 (3.59) & 0.35 & 0.69 & aliphatic, aliphatic \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Main physicochemical characteristics attributed to the dipeptides under study. As presented in Figure 1, an identity of 94.01% was estimatedbetween _Rattus norvegicus_ mGluR1 (PDB ID: 1 EWK) and _Homo sapiens_ mGluR1 (PDB ID: 3 KS9). Only a few mismatches were found at positions apparently not belonging to key residues of the binding site, suggesting that the motif is evolutionarily conserved [58]. Based on their signal transduction pathways and pharmacological properties, mGluRs have been categorized into three groups: Group I (mGluR1 and mGluR5) are normally stimulatory and associated with phospholipase C activation and second messengers, such as inositol and diacylglycerol production. Group II (mGluR2 and mGluR3) and Group III (mGluR4, mGluR6, mGluR7, and mGluR8) normally inhibit glutamatergic neurotransmission and they are both negatively coupled to adenylyl cyclase [59]. The N terminus of mGluRs comprises a large extracellular E-binding domain and the cytoplasmic C terminus of mGluRs participates in interactions with G proteins [25]. The taste receptor mGluR1 has been found in rat circumvalate and foliate papillae of the posterior tongue, in a truncated form compared to its homologous expressed in the brain. Its activation depends on the disulfide-linked homodimer conformation, and signalization probably occurs through IP3 formation and Ca2+ release from intracellular stores, but only at concentrations \(\geq\)1 mmol E [60]. The bi-lobed protomer architectures flexibly change their domain arrangements to form an \"open\" or \"closed\" conformation. Upon agonist binding, the protomer is closed at the cleft between the two ligand-binding sites, conformations, which are referred to as closed and open forms. However, the actual conformation in the physiological state is still unknown [61]. To our knowledge, there is only a structure linked to the Human mGluR1 determined, with an open-open conformation (PDB ID: 3 KS9), while the most studied _Rattus norvegicus_ mGluR1 structure published to date consists of a closed-open conformation (PDB ID: 1 EWK). Other structures from this last publication are an open-open conformation (PDB ID: 1 EWT) and a closed-open conformation in the ligand free form (PDB ID: 1 EWV) [61; 62].