scholarly journals Mechanism of mutual activation of the tryptophan synthase alpha and beta subunits. Analysis of the reaction specificity and substrate-induced inactivation of active site and tunnel mutants of the beta subunit.

1991 ◽  
Vol 266 (32) ◽  
pp. 21548-21557 ◽  
Author(s):  
S.A. Ahmed ◽  
S.B. Ruvinov ◽  
A.M. Kayastha ◽  
E.W. Miles
Keyword(s):  
Active Site ◽  
Beta Subunit ◽  
Beta Subunits ◽  
Tryptophan Synthase ◽  
Reaction Specificity

scholarly journals Substitution of a Surface-Exposed Residue Involved in an Allosteric Network Enhances Tryptophan Synthase Function in Cells

2021 ◽  
Vol 8 ◽  
Author(s):  
Rebecca N. D’Amico ◽  
Yuliana K. Bosken ◽  
Kathleen F. O’Rourke ◽  
Alec M. Murray ◽  
Woudasie Admasu ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Molecular Dynamics ◽  
Active Site ◽  
Beta Subunit ◽  
Alpha Subunit ◽  
Tryptophan Synthase ◽  
Wild Type ◽  
Auxotrophic Strain ◽  
Hydrophobic Tunnel ◽  
Dynamics Simulations

Networks of noncovalent amino acid interactions propagate allosteric signals throughout proteins. Tryptophan synthase (TS) is an allosterically controlled bienzyme in which the indole product of the alpha subunit (αTS) is transferred through a 25 Å hydrophobic tunnel to the active site of the beta subunit (βTS). Previous nuclear magnetic resonance and molecular dynamics simulations identified allosteric networks in αTS important for its function. We show here that substitution of a distant, surface-exposed network residue in αTS enhances tryptophan production, not by activating αTS function, but through dynamically controlling the opening of the indole channel and stimulating βTS activity. While stimulation is modest, the substitution also enhances cell growth in a tryptophan-auxotrophic strain of Escherichia coli compared to complementation with wild-type αTS, emphasizing the biological importance of the network. Surface-exposed networks provide new opportunities in allosteric drug design and protein engineering, and hint at potential information conduits through which the functions of a metabolon or even larger proteome might be coordinated and regulated.

scholarly journals Comparison of liver glycosylasparaginases from six vertebrates

1992 ◽  
Vol 282 (3) ◽  
pp. 891-897 ◽  
Author(s):  
O K Tollersrud ◽  
N N Aronson
Keyword(s):  
Amino Acids ◽  
Reaction Mechanism ◽  
Basic Structure ◽  
Low Ph ◽  
Beta Subunit ◽  
Beta Subunits ◽  
Species Identity ◽  
Closely Related Species ◽  
Human Enzyme ◽  
Specific Antisera

Structural and physical properties of glycosylasparaginase (EC 3.5.1.26) from the livers of human, pig, cow, rat, mouse and chicken were compared. The enzyme in all species had a common basic structure of two N-glycosylated subunits of about 24 (alpha) and 20 (beta) kDa joined by non-covalent forces. Subunit-specific antisera against the rat glycosylasparaginase bound specifically and sensitively to the corresponding subunits from all species. Identity of 80% of the amino acids was found between the N-terminal sequences of corresponding pig and rat glycosylasparaginase alpha- and beta-subunits and the deduced sequence from a human glycosylasparaginase cDNA [Fisher, Tollersrud & Aronson (1990) FEBS Lett. 269, 440-444]. The beta-subunit from all three species has an N-terminal threonine reported to be involved in the reaction mechanism for the human enzyme [Kaartinen, Williams, Tomich, Yates, Hood & Mononen (1991) J. Biol. Chem. 266, 5860-5869]. The native enzyme appeared as a heterodimer among the mammals, whereas the chicken enzyme had a greater molecular mass and is probably either a tetramer or a heterodimer bound to an unrelated peptide(s). All glycosylasparaginases were thermostable, requiring temperatures between 65 degrees C and 80 degrees C to be irreversibly inactivated. In addition, they were unusually stable at high pH and remained active in the presence of SDS except at low pH. The pH maximum was between 5.5 and 6 except for the rat and mouse enzymes which had a broad maximum between pH 7 and 8. A number of other properties were observed which also distinguish the enzyme from individual and closely related species.

scholarly journals Insulin and insulinlike growth factor 1 (IGF-1) receptors during central nervous system development: expression of two immunologically distinct IGF-1 receptor beta subunits.

1989 ◽  
Vol 9 (7) ◽  
pp. 2806-2817 ◽  
Author(s):  
R S Garofalo ◽  
O M Rosen
Keyword(s):  
Growth Factor ◽  
Tyrosine Kinase ◽  
System Development ◽  
Fetal Brain ◽  
Nervous System Development ◽  
Adult Brain ◽  
Beta Subunit ◽  
Tyrosine Kinase Domain ◽  
Beta Subunits ◽  
Insulinlike Growth Factor

Insulin and insulinlike growth factor 1 (IGF-1) receptors are present in brain, yet their function remains obscure. Expression of these tyrosine kinase-bearing growth factor receptors during rat brain development was examined by using three antipeptide antibodies directed against epitopes in the beta subunits (AbP2, AbP4, and AbP5). All three antibodies recognized both insulin and IGF-1 receptors. Membranes were prepared from fetal brains (14 to 21 days of gestation), neonatal brain (postnatal day 1), and adult brain. Immunoblot analyses using AbP4 and AbP5 revealed a 92-kilodalton (kDa) protein that corresponded to the beta subunit of the insulin and IGF-1 receptors. Densitometric scanning of immunoblots indicated that receptor proteins were 4- to 10-fold more abundant in fetal brain membranes than in membranes from adult brain. Expression was highest during 16 to 18 days of gestation and declined thereafter to the relatively low level found in adult brain. Immunoblot analyses with AbP2 as well as ligand-activated receptor autophosphorylation revealed an additional protein of 97 kDa. This protein was phosphorylated in response to IGF-1 and was not directly recognized by AbP4 or AbP5. The covalent association of the 97-kDa protein with the 92-kDa beta subunit was indicated by the ability of AbP4 and AbP5 to immunoprecipitate both proteins under nonreducing conditions but only the 92-kDa protein after reduction. In contrast, AbP2 immunoprecipitated both proteins regardless of their association. This immunospecificity remained unchanged after deglycosylation of the isolated proteins. Two-dimensional tryptic phosphopeptide analysis showed that the 92- and 97-kDa subunits of the IGF-1 receptor are related but distinct proteins. Taken together, the data suggest that the 92- and 97-kDa subunits differ in primary amino acid sequence. Thus, two distinct beta subunits may be present in a single IGF-1 receptor in brain. These subunits have in common an epitope recognized by an antibody to the tyrosine kinase domain (AbP2) but differ in regions thought to be important in receptor kinase regulation and signal transduction.

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