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In honor of the 4th of July, our #MOTW acts as a colorful “firework” display in biology. Known as Red Fluorescent Protein (RFP; PDB ID: 2VAD), it fluoresces with a red-orange color when excited by light at a certain range of wavelengths. RFP was developed through directed mutagenesis of our prior MOTW – Green Fluorescent Protein (https://www.instagram.com/p/BB0i7TRQu9T). Common use is to include the gene for RFP production in a plasmid along with another gene to be expressed. The plasmid is inserted into a colony of E. coli. The colonies then propagate and, those that fluoresce, reveal colonies that have multiplied with RFP and the target gene.

Porins are a class of transmembrane proteins that passively channel hydrophilic (water loving) molecules of various sizes into and out of the cell. This process is necessary to remove toxins and absorb nutrients and substrates for survival. Transmembrane proteins have two basic structures – alpha-helical and beta-barrels. Porins are of the latter which consist of eight to twenty-two beta-strands laid end to end in a spiral-like pattern as can be seen in the attached rendering (PDB: 2X9K, substrate in green). The residue sequence of these beta-strands is unique in that they have polar residues facing the aqueous channel and non-polar residues facing the interior of the protein. Residue sidechains within the channel determine the specificity of individual porins.

Have you ever wondered why there is a sign reminding employees to wash their hands in public restrooms? This is a practice that our mothers tried to teach us as young kids. Salmonella Typhimurium, much like all other species of the genus Salmonella, naturally live within the gastrointestinal system of both animals and humans. More specifically Salmonella thrives within the intestinal tract as it is not made to withstand the high acidity of the stomach. The pathogenesis of Salmonella begins when contact with contaminated food or water occurs. Contamination occurs through contact of fecal matter with food or water! Often, this happens due to lack of proper hygiene (washing our hands) or when insects, primarily flys, move from fecal matter to a food source. Salmonella will make use of glucose that it finds within the host’s body. The replication processes of Salmonella Typhimurium are very typical of most bacteria - undergoing fission. However, the location that this occurs is unique to Salmonella in that it will insert itself into host cells within a salmonella containing vacuole. In doing this, it creates an environment that will provide it with many of the needed nutrients for replication. PDB 1A0S is the X-ray structure of a sucrose-specific porin (ScrY) from Salmonella typhimurium.

Summer break is here, and with that comes vacations, internships, and sun exposure! With increased sun exposure, our melanocytes are working overtime to produce melanin, a pigment in our skin that is responsible for UV light protection and is the reason we tan. This molecule, tyrosinase related protein 1 (TYRP1) (PDB 5M8L), is one of three glycoenzymes that are key to melanin production. This protein contains two zinc ions at the active site, differing from copper ions other tyrosinases have, that are believed to be responsible for its role in melanin production [1]. Without this melanosomal protein, our skin wouldn’t be able to protect itself from harmful UV rays that can be responsible for mutations in our DNA - which can lead to skin cancer. TYRP1 mutations are linked to a type of albinism in humans called oculocutaneous albinism type 3 [2].

One of the key molecular machines used in protein synthesis is our old MOTW - the ribosome (https://t.co/fGq5mtKmKp). Ribosomes are composed of a large subunit and small subunit (pictured here: PDB 4V5O). The small subunit binds to initiation factors and screens for messenger RNA (mRNA) to begin protein synthesis. The small subunit then allows the large subunit to form proteins. The ribosome is well studied, which is why there is no reason protein synthesis must be constricted to the inside of the cell. Using this well-understood and highly-regulated process we can program protein synthesis and remove any need to grow-up cells – essentially saving days of lab time for every protein!

Clathrins are proteins with a unique triskelion shape (PDB ID 1XI4) that functions as a coating for vesicles, which are small containers responsible for transporting proteins and small molecules throughout the cell. Clathrin proteins attach to signal proteins that are embedded in a membrane and form a polyhedral lattice, pinching off a sphere of membrane and trapping proteins and small molecules inside.

Galactokinase (pictured here, PDB: 1PIE) is critical in the phosphorylation of alpha-D-galactose to galactose 1-phosphate in the Leloir pathway. This is the pathway for metabolizing D-galactose - also known as "milk sugar", though galactose is found in fruits and vegetables and formed when glycoproteins and glycolipids are broken down within the body. Mutations of the gene that code for galactokinase result in a disease called Galactosemia where galactose accumulates. This is not to be confused with lactose intolerance - which is a much milder disorder! Undiagnosed Galactosemia leads to speech deficits, Ataxia, Dysmetria, diminished bone density, and early onset cataracts.

The way we learn new things and retain memories makes up a large part of who we are. To make these tasks possible, our central nervous system relies heavily on neurons and neurotransmitters. Glutamate (Glu) is one of the primary neurotransmitters used in synaptic connections between neurons. By coordinating glutamate at the synaptic cleft with a variety of neuron-bound glutamate receptors - such as AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptors - the nervous system can carry out its daily tasks. As a dynamic mechanism, Glu traveling to AMPA receptors to generate a response can be thought of as pollen (transmitter) landing on a flower (receptor) to enable reproduction (response). Glu and AMPA receptors don't always work perfectly though, and their dysfunction can be seen in many neurodegenerative disorders including Parkinson's, Alzheimer's, epilepsy, and dementia. Many structural biology studies in the past decade have focused heavily on looking at competitive inhibitors to block glutamate from binding and counter instances of hyperactive AMPA receptors, hoping to mitigate the effects of some of these neurological issues. Shown here is the binding portion of an AMPA receptor (GluR2) bound to glutamate. (PDB ID: 3DP6)

Lysosomes are organelles within cells that break down molecules by use of lysosomal enzymes. This function is important to many biological systems. As part of waste management, the enzymes break apart malfunctioning or unnecessary proteins into their constituent amino acids for reuse. This saves energy as the cell won’t have to acquire new amino acids nor remove the malfunctioning proteins through more complicated means. (PDB 3LX9)

macromoltek Iron (Fe) is an essential element for almost every living organism as it participates in the synthesis of important proteins like myoglobin and hemoglobin. Despite its important role, free iron is highly toxic for cells as it can form free radicals from reactive oxygen species [1]. Luckily for us, highly regulated mechanisms have evolved to transport this important molecule throughout the body. Ferritin (PDB 1MFR) is a globular protein with a critical role in iron homeostasis as it stores this element in a soluble and non-toxic form. The iron-free ferritin protein is called apoferritin. This protein forms a spherical-shaped container composed of 24 subunits, which can be of either type H or L. The main functions of ferritin are to sequester free ferrous iron, Fe(II), and to convert it into the ferric state, Fe(III). The non-toxic form of iron is then transported by ferritin to areas of the body where it is required [2].