Fundamentals of Protein Structure

Our life is maintained by molecular network systems Molecular network system in a cell (From ExPASy Biochemical Pathways; http://www.expasy.org/cgi-bin/show_thumbnails.pl?2)

Proteins play key roles in a living system Three examples of protein functions Catalysis: Almost all chemical reactions in a living cell are catalyzed by protein enzymes. Transport: Some proteins transports various substances, such as oxygen, ions, and so on. Information transfer: For example, hormones. Alcohol dehydrogenase oxidizes alcohols to aldehydes or ketones Haemoglobin carries oxygen Insulin controls the amount of sugar in the blood

Amino acid: Basic unit of protein COO- NH3+ C R H Different side chains, R, determin the properties of 20 amino acids. Amino group Carboxylic acid group An amino acid

White: Hydrophobic, Green: Hydrophilic, Red: Acidic, Blue: Basic 20 Amino acids Glycine (G) Alanine (A) Valine (V) Isoleucine (I) Leucine (L) Proline (P) Methionine (M) Phenylalanine (F) Tryptophan (W) Asparagine (N) Glutamine (Q) Serine (S) Threonine (T) Tyrosine (Y) Cysteine (C) Asparatic acid (D) Glutamic acid (E) Lysine (K) Arginine (R) Histidine (H) White: Hydrophobic, Green: Hydrophilic, Red: Acidic, Blue: Basic

Proteins are linear polymers of amino acids NH3＋ C COOー ＋ NH3＋ C COOー ＋ H H A carboxylic acid condenses with an amino group with the release of a water H2O H2O R1 R2 R3 NH3＋ C CO NH C CO NH C CO H Peptide bond H Peptide bond H The amino acid sequence is called as primary structure F T D A G S K A N G S

Amino acid sequence is encoded by DNA base sequence in a gene DNA molecule DNA base sequence ・ C G A T ＝

Amino acid sequence is encoded by DNA base sequence in a gene Second letter T C A G First letter TTT Phe TCT Ser TAT Tyr TGT Cys Third letter TTC TCC TAC TGC TTA Leu TCA TAA Stop TGA TTG TCG TAG TGG Trp CTT CCT Pro CAT His CGT Arg CTC CCC CAC CGC CTA CCA CAA Gln CGA CTG CCG CAG CGG ATT Ile ACT Thr AAT Asn AGT ATC ACC AAC AGC ATA ACA AAA Lys AGA ATG Met ACG AAG AGG GTT Val GCT Ala GAT Asp GGT Gly GTC GCC GAC GGC GTA GCA GAA Glu GGA GTG GCG GAG GGG

Gene is protein’s blueprint, genome is life’s blueprint DNA Genome Gene Gene Protein Protein

Gene is protein’s blueprint, genome is life’s blueprint Glycolysis network Genome Gene Protein

In 2003, Human genome sequence was deciphered! Genome is the complete set of genes of a living thing. In 2003, the human genome sequencing was completed. The human genome contains about 3 billion base pairs. The number of genes is estimated to be between 20,000 to 25,000. The difference between the genome of human and that of chimpanzee is only 1.23%! 3 billion base pair => 6 G letters & 1 letter => 1 byte The whole genome can be recorded in just 10 CD-ROMs!

Each Protein has a unique structure Amino acid sequence NLKTEWPELVGKSVEEAKKVILQDKPEAQIIVLPVGTIVTMEYRIDRVRLFVDKLDNIAEVPRVG Folding!

Basic structural units of proteins: Secondary structure α-helix β-sheet Secondary structures, α-helix and β-sheet, have regular hydrogen-bonding patterns.

Three-dimensional structure of proteins Tertiary structure Quaternary structure

Hierarchical nature of protein structure Primary structure (Amino acid sequence) ↓ Secondary structure （α-helix, β-sheet） Tertiary structure （Three-dimensional structure formed by assembly of secondary structures） Quaternary structure （Structure formed by more than one polypeptide chains）

Close relationship between protein structure and its function Example of enzyme reaction Hormone receptor Antibody substrates A enzyme enzyme B Matching the shape to A Digestion of A! enzyme A Binding to A

Protein structure prediction has remained elusive over half a century “Can we predict a protein structure from its amino acid sequence?” Now, impossible!

Summary Proteins are key players in our living systems. Proteins are polymers consisting of 20 kinds of amino acids. Each protein folds into a unique three-dimensional structure defined by its amino acid sequence. Protein structure has a hierarchical nature. Protein structure is closely related to its function. Protein structure prediction is a grand challenge of computational biology.