diff --git a/Project.toml b/Project.toml
index 37dfbc1..8c9db0c 100644
--- a/Project.toml
+++ b/Project.toml
@@ -17,7 +17,7 @@ Zygote = "e88e6eb3-aa80-5325-afca-941959d7151f"
 ZygoteIdealizationExt = ["Zygote"]
 
 [compat]
-BioStructures = "3"
+BioStructures = "4"
 LinearAlgebra = "1"
 PrecompileTools = "1"
 Rotations = "1"
diff --git a/src/protein/pdb.jl b/src/protein/pdb.jl
index 0eba779..9fb8184 100644
--- a/src/protein/pdb.jl
+++ b/src/protein/pdb.jl
@@ -53,7 +53,7 @@ function Protein.Chain(chain::BioStructures.Chain; res_selector=backboneselector
     return Protein.Chain(residues)
 end
 
-function chains(struc::BioStructures.ProteinStructure; res_selector=backboneselector)
+function chains(struc::BioStructures.MolecularStructure; res_selector=backboneselector)
     chains = Protein.Chain[]
     for model in struc, chain in model
         isempty(chain) || push!(chains, Protein.Chain(chain, res_selector=res_selector))
@@ -68,7 +68,7 @@ Loads a protein (represented as a `Vector{Protein.Chain}`) from a PDB file.
 Assumes that each residue starts with three atoms: N, CA, C.
 """
 function readpdb(pdbfile::String)
-    struc = read(pdbfile, BioStructures.PDB)
+    struc = read(pdbfile, BioStructures.PDBFormat)
     return chains(struc)
 end