DOPA decarboxylase: Difference between revisions

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====Quaternary Structure====

The level of protein structure exists solely in multisubunit complexes. DOPA decarboxylase is a homodimeric enzyme with the active site located near the monomer-monomer interface, thus highlighting the importance of this level of protein structure to the enzymes function. Furthermore, since the N-terminal domain of one monomer packs on top of the other monomer, resulting in an extended dimer interface, this level of tertiary structure is most likely stable only in the dimeric form of the enzyme.

===Helix Capping===

====Helix Capping====

The α helix is characterized by main chain hydrogen bonds between the C=O of residue n and the NH of residue n+4. All residues in the helix participate in this type of hydrogen bonding except the first NH groups and the last C=O groups at the ends of the helix. Helix-capping motifs are specific hydrogen bonding and hydrophobic interactions found at the ends of helices. Seven distinct capping motifs have been identified; three at the N-terminus and four at the C-terminus. Shown below is the '''capping-box''' motif found at the end of the helix composed of residues 147-171. [[image:ncap2.png|thumb|center|400px|'''capping-box''']]Here, Ncap is Ser-147. The hydroxyl oxygen of Ser-147 forms a standard Ncap hydrogen bond with the amide of N3 (Glu-150), and the side chain carbonyl oxygen of Glu-150 forms a hydrogen bond with the amide of Ser-147. This form of special capping satisfies two of the four non hydrogen-bonded helix N-terminal amides. The side-chain capping apparent here is typical at the N-terminus. According to Aurora and Rose, this would be termed a motif Ib, N`-> N4 motif. Thus, the important hydrophobic interaction occurs between N` (Gly-146) and N4 (Ala-151).

The α helix is characterized by main chain hydrogen bonds between the C=O of residue n and the NH of residue n+4. All residues in the helix participate in this type of hydrogen bonding except the first NH groups and the last C=O groups at the ends of the helix. Helix-capping motifs are specific hydrogen bonding and hydrophobic interactions found at the ends of helices. Seven distinct capping motifs have been identified; three at the N-terminus and four at the C-terminus. Shown below is the '''capping-box''' motif found at the end of the helix composed of residues 147-171. Here, Ncap is Ser-147. The hydroxyl oxygen of Ser-147 forms a standard Ncap hydrogen bond with the amide of N3 (Glu-150), and the side chain carbonyl oxygen of Glu-150 forms a hydrogen bond with the amide of Ser-147. This form of special capping satisfies two of the four non hydrogen-bonded helix N-terminal amides. The side-chain capping apparent here is typical at the N-terminus. According to Aurora and Rose, this would be termed a motif Ib, N`-> N4 motif. Thus, the important hydrophobic interaction occurs between N` (Gly-146) and N4 (Ala-151).

DOPA decarboxylase: Difference between revisions

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@@ Line 34: / Line 34: @@
 ====Quaternary Structure====
 The level of protein structure exists solely in multisubunit complexes. DOPA decarboxylase is a homodimeric enzyme with the active site located near the monomer-monomer interface, thus highlighting the importance of this level of protein structure to the enzymes function. Furthermore, since the N-terminal domain of one monomer packs on top of the other monomer, resulting in an extended dimer interface, this level of tertiary structure is most likely stable only in the dimeric form of the enzyme.
+===Helix Capping===
-====Helix Capping====
+The α helix is characterized by main chain hydrogen bonds between the C=O of residue n and the NH of residue n+4. All residues in the helix participate in this type of hydrogen bonding except the first NH groups and the last C=O groups at the ends of the helix. Helix-capping motifs are specific hydrogen bonding and hydrophobic interactions found at the ends of helices. Seven distinct capping motifs have been identified; three at the N-terminus and four at the C-terminus. Shown below is the '''capping-box''' motif found at the end of the helix composed of residues 147-171. [[image:ncap2.png|thumb|center|400px|'''capping-box''']]Here, Ncap is Ser-147. The hydroxyl oxygen of Ser-147 forms a standard Ncap hydrogen bond with the amide of N3 (Glu-150), and the side chain carbonyl oxygen of Glu-150 forms a hydrogen bond with the amide of Ser-147. This form of special capping satisfies two of the four non hydrogen-bonded helix N-terminal amides. The side-chain capping apparent here is typical at the N-terminus. According to Aurora and Rose, this would be termed a motif Ib, N`-> N4 motif. Thus, the important hydrophobic interaction occurs between N` (Gly-146) and N4 (Ala-151).
-The α helix is characterized by main chain hydrogen bonds between the C=O of residue n and the NH of residue n+4. All residues in the helix participate in this type of hydrogen bonding except the first NH groups and the last C=O groups at the ends of the helix. Helix-capping motifs are specific hydrogen bonding and hydrophobic interactions found at the ends of helices. Seven distinct capping motifs have been identified; three at the N-terminus and four at the C-terminus. Shown below is the '''capping-box''' motif found at the end of the helix composed of residues 147-171. Here, Ncap is Ser-147. The hydroxyl oxygen of Ser-147 forms a standard Ncap hydrogen bond with the amide of N3 (Glu-150), and the side chain carbonyl oxygen of Glu-150 forms a hydrogen bond with the amide of Ser-147. This form of special capping satisfies two of the four non hydrogen-bonded helix N-terminal amides. The side-chain capping apparent here is typical at the N-terminus. According to Aurora and Rose, this would be termed a motif Ib, N`-> N4 motif. Thus, the important hydrophobic interaction occurs between N` (Gly-146) and N4 (Ala-151).