Reversible Binding of the Chemoattractant Folic Acid to Cells of Dictyostelium discoideum

Abstract

The chemoattractant folic acid binds reversibly to receptors at the surface of Dictyostelium cells. In undifferentiated cells (to.5) 6 x lo4 binding sites per cell with a Ko.S value of 1.5 x M were determined. The number of folic acid receptors per cell decreases slightly during cell development. In differentiated cells (tlo) 3.3 x lo4 binding sites per cell were estimated. The folic acid binding sites appear to be specific for folic acid and its derivatives. 2-Deamino-2-hydroxyfolic acid, 4-aminofolic acid (aminopterin), and 4-amino-10-methylfolic acid (aniethopterin) compete for the folic-acidbinding sites. Pterins, p-aniinobenzoic acid and glutamic acid show no significant competition for the folic-acid-binding sites. Nor do adenosine 3',5'-phosphate and guanosine 3',5'-phosphate affect binding of folic acid. The folic acid receptors appear to be distinct from the catalytic sites of the membrane-bound folic acid deaminase.Cells of Dictyostelium discoideum react chemotactically to cyclic AMP [l] as well as to folic acid and pterins [2,3] We investigated the binding of folic acid to cells of D. discoideum and provide evidence for the presence of folic acid receptors at the cell's surface. The number of folic acid receptors per cell decreases slightly during cell development. The receptors appear to be specific: folic acid derivatives compete for the folic-acid-binding sites, but pterins do not compete. Also cyclic nucleotides do not influence binding of folic acid. An account of this work was published in abstract form [ll].

cAMP induces a rapid and reversible modification of the chemotactic receptor in Dictyostelium discoideum.

“…10-5-10 -6 folic acid, 10-4M Ca +*, or 7 x 10-TM Ca ++ ionophore A23187 (tested in the absence or presence of Ca ++) did not increase the phosphorylation ofpP47 or induce the P47 form of the receptor. Folic acid, a chemoattractant for undifferentiated cells appears to function via its own surface receptor, whereas Ca *+ and its ionophore may affect development by increasing the number of cAMP binding sites on the cell surface (17)(18)(19). ConA has been shown to cause patching, capping, and endocytosis of ConA receptors on D. discoideum (20).…”

High fidelity information processing in folic acid chemotaxis ofDictyosteliumamoebae

“…is done in the approximate range where we detected the greatest violation of the data processing inequality (c 0 ¼ 5000 nM [16,18].…”

Fluorescent products secreted by Dictyostelium discoïdeum cells which are able to aggregate

“…Folate receptors have also been shown on the cell surface [16]. Furthermore, amino and amethopterin [2] interact with the same folate receptors [16,17], but are not degraded by the 2-folate deaminase [ 17]. Folic acid, long considered as a mere chemio-attractant, is now suggested as being somewhat interchangeable with the other chemio-attractant cAMP, an important mediator of the aggregation competence, and both extracellular signals could share a common cellular pathway of signal transduction [ 18,19].…”

“…However, the 2-folate deaminase activity and location have been followed during development: it mimics cAMP phosphodiesterase in its regulatory function [ 14,15]. Folate receptors have also been shown on the cell surface [16]. Furthermore, amino and amethopterin [2] interact with the same folate receptors [16,17], but are not degraded by the 2-folate deaminase [ 17].…”

“…Many such factors have been shown for Dictyosteliurn, as the effector of N-acetylglucosaminidase biosynthesis [4], the factor necessary for differentiation in submerged clumps [5], the DIF (differentiation inducing factor) [16], which now turns out to be essential for stalk cell differentiation [7], that AIF (aggregation inhibiting factor) [8], existing in growing cells and developmentally regulated and the STF (slug turning factor) [9,10], involved in phototaxis and thermotaxis. None of these factors has been identified up to now.…”