Arylsulfatase B is an enzyme

Enzyme

Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

 associated with mucopolysaccharidosis VI

Mucopolysaccharidosis VI

Maroteaux–Lamy syndrome is a form of mucopolysaccharidosis caused by a deficiency in arylsulfatase B...

.

Arylsulfatase B is among a group of arylsulfatase

Arylsulfatase

Arylsulfatase is a type of sulfatase enzyme.Types include:*Arylsulfatase A *Arylsulfatase B *Steroid sulfatase *ARSC2*ARSD*ARSE...

 enzymes present in the lysosomes of the liver

Liver

The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...

, pancreas

Pancreas

The pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as a digestive organ, secreting pancreatic juice containing digestive enzymes that assist...

, and kidney

Kidney

The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...

s of animals. The purpose of the enzyme is to hydrolyze sulfates in the body. ARSB does this by breaking down Glycosaminoglycan

Glycosaminoglycan

Glycosaminoglycans or mucopolysaccharides are long unbranched polysaccharides consisting of a repeating disaccharide unit. The repeating unit consists of a hexose or a hexuronic acid, linked to a hexosamine .-Production:Protein cores made in the rough endoplasmic reticulum are posttranslationally...

s(GAGs), which are large sugar molecules in the body. ARSB targets two GAGs in particular: dermatan sulfate

Dermatan sulfate

Dermatan sulfate is a glycosaminoglycan found mostly in skin, but also in blood vessels, heart valves, tendons, and lungs....

 and chondroitin sulfate

Chondroitin sulfate

Chondroitin sulfate is a sulfated glycosaminoglycan composed of a chain of alternating sugars . It is usually found attached to proteins as part of a proteoglycan. A chondroitin chain can have over 100 individual sugars, each of which can be sulfated in variable positions and quantities...

.

Over 130 mutations to ARSB have been found, each leading to a deficiency in the body. In most cases, the mutation occurs on a single nucleotide

Nucleotide

Nucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...

 in the sequence. An arylsulfatase B deficiency can lead to an accumulation of GAGs in lysosomes, which in turn can lead to Maroteaux–Lamy syndrome, or mucopolysaccharidosis VI.

Structure

The primary structure of Escherichia coli

Escherichia coli

Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...

arylsulfatase B contains a primary sequence of 502 amino acids. Its secondary structure is quite complex, containing numerous alpha helices

Alpha helix

A common motif in the secondary structure of proteins, the alpha helix is a right-handed coiled or spiral conformation, in which every backbone N-H group donates a hydrogen bond to the backbone C=O group of the amino acid four residues earlier...

 (20 total containing 138 residues) and beta sheet

Beta sheet

The β sheet is the second form of regular secondary structure in proteins, only somewhat less common than the alpha helix. Beta sheets consist of beta strands connected laterally by at least two or three backbone hydrogen bonds, forming a generally twisted, pleated sheet...

s (21 strands total containing 87 residues). The functional enzyme is believed to be a homo tetramer

Tetramer

A tetramer is a protein with four subunits . There are homotetramers such as glutathione S-transferase or single-strand binding protein, dimers of hetero-dimers such as hemoglobin , and heterotetramers, where each subunit is different.-Subunit interactions in tetramers:The interactions between...

. Due to the complexity of arylsulfatase B's secondary structure, many hydrophobic and hydrophilic regions are present, as demonstrated by the Kyte-Doolittle hydropathy plot:
Additional structural data is shown in Ramachandran analysis plots at: http://www.rcsb.org/pdb/images/3ED4_ram_m_500.pdf.

External links

• Medical Dictionary, Arylsulfatase B function.
• Protein Data Base (PDB), Arylsulfatase structure.
• Genetics Home Reference, Arylsulfatase B function.