JsonUtility with openweatherAPI

Here's my JSON API in:

http://api.openweathermap.org/data/2.5/weather?q=Vietnam,vn≈pid=0ab6a57ce5d39ea31b0ecd53db35edf4&mode=json⟨=en

 {
     coord: {
     lon: 105.85,
     lat: 21.03
     },
     weather: [
     {
     id: 800,
     main: "Clear",
     description: "clear sky",
     icon: "01n"
     }
     ],
     base: "stations",
     main: {
     temp: 297.897,
     pressure: 1009.91,
     humidity: 92,
     temp_min: 297.897,
     temp_max: 297.897,
     sea_level: 1018.33,
     grnd_level: 1009.91
     },
     wind: {
     speed: 1.93,
     deg: 181.501
     },
     clouds: {
     all: 0
     },
     dt: 1469311176,
     sys: {
     message: 0.0124,
     country: "VN",
     sunrise: 1469226442,
     sunset: 1469273919
     },
     id: 1561096,
     name: "Xóm Pho",
     cod: 200
     }

Here's my classes:

WeatherData.cs

 [System.Serializable]
 public class WeatherData {
     public Coord cord;
 
     public Weather[] weather;
 
     public string @base;
 
     public Main main;
 
     public Wind wind;
 
     public Clouds clouds;
 
     public uint dt;
 
     public Sys sys;
 
     public int id;
 
     public string name;
 
     public int cod;
 
     public void Load(string savedData)
     {
         JsonUtility.FromJsonOverwrite(savedData, this);
     }
 }

Coord.cs

 [System.Serializable]
 public class Coord
 {
     public float lon;
     public float lat;
 }

Other classes (Weather, Base, Main ...) worked fine. But when serialized Coord object, value of lon and lat not correct (lon = lat = 0.0f). Can somebody explain me why?